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Mushroom Onion Grilled Cheese

If you're in need of a great vegetarian lunch, make sure to SAVE or print for later this Mushroom Onion Grilled Cheese sandwich recipe! It's full of earthy umami flavor thanks to sauteed sliced mushrooms and onions, and it's got that irresistible melty cheese pull situation going on. Enjoy the crisp, buttery crust and the cheesy melty savory inside.

This sandwich is great on its own, but even better paired with a light side salad or spring soup.

Two mushroom grilled cheese sandwiches stacked on top of each other
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Mushroom grilled cheese

I'm a big fan of mushrooms paired with creamy or cheesy flavors, such as these creamy mushroom pork chops or this creamy chicken and mushroom skillet. So it was only a matter of time until I took delicious sauteed mushrooms and onions and paired them with loads of cheesy in the perfect mushroom grilled cheese sandwich!

I cook this grilled cheese in melted better for the most flavorful, crispy buttery outside. Another option is to brush mayonnaise on the outside of the bread and cook the grilled cheese that way. Both turn out amazing! 

Two mushroom onion grilled cheese sandwiches being pulled apart

I used mozzarella for this sandwich for ultimate cheese meltiness, but you can use any melt-able cheese that you like. A combination of smoked mozzarella, smoked provolone, or smoked white cheddar and gouda is also amazing. 

Play around and figure out which cheese combinations you like the most for this easy sandwich!

Close up of a mushroom grilled cheese sandwich cut in half to show texture inside

More unique grilled cheese ideas: Pickle Grilled Cheese

Ingredients

  • 3 cups baby bella mushrooms, cleaned and sliced (about a 10-16 oz package)
  • 1 yellow onion, thinly sliced into half moons
  • 1 teaspoon salt, or to taste
  • ¼ - ½ teaspoon ground black pepper, to taste
  • 3 tablespoons butter (or substitute with olive oil)
  • 2 tablespoons fresh parsley leaves, finely minced
  • 4 slices bread (sliced white bread, such as brioche, sourdough, or Texas toast, but whole wheat is also a great option!)
  • 2-4 slices mozzarella cheese (or use any combination of mozzarella, provolone, white cheddar, gouda... or try smoked versions of each of these cheeses!)

More unique grilled cheese sandwiches: BBQ Chicken Grilled Cheese

Equipment

  • 1-2 pans (To cook two sandwiches at a time, you'll need a large pan (12-14 inch) or two smaller pan. You can also decide whether to cook the mushroom sandwich in the same pan where you sauteed the onions and mushrooms, or to clean it out, or cook it in a separate pan. It's up to you!)
  • A bowl to mix the mushrooms and onions
  • Tongs and wet paper towels to clean out the pan

More grilled cheese sandwiches to try: Blackberry Goat Cheese Grilled Cheese

Instructions

Heat a large pan over medium heat. Add 2 tablespoons of butter (reserve the rest for later!), sliced onion, salt, and pepper. Sauté for about 20 minutes and let the onions caramelize without burning. If needed add a few tablespoons of water to prevent burning.

Collage of 2 pictures showing how to caramelize onions

Remove the onions to a bowl, and add the mushrooms. Turn up the heat and cook over medium-high heat for 5-7 minutes or until cooked down to your liking, stirring constantly.

Sauteed mushrooms in a pan

Add the mushrooms to the bowl with the onions, or add the onions to the mushrooms. Add the parsley, and stir everything together.

Sauteed mushrooms and onions mixture in a pan

Assemble your sandwiches: place 1 slice of cheese on your bread. Top with half the mushroom mixture. If using more cheese, top the mushroom mixture with another slice, and top with the other bread. 

Use tongs and a damp paper towel to wipe down the skillet. Melt the butter in the pan and cook the sandwiches until the bread is golden brown and the cheese is melted.

Collage of 2 pictures showing how to cook a mushroom grilled cheese

If cooking both sandwiches in 1 large pan, melt about ½ tablespoon of butter in the pan, cook on one side, then add the rest of the butter and cook on the other side. If using two smaller pans, use about ¼ tablespoon butter for each side of the sandwich.

More grilled cheese recipes to try: Pear Balsamic Goat Cheese Grilled Cheese

Recipe variations and tips

  • As mentioned above, smoked sliced cheese is an AWESOME addition to this sandwich.
  • Add a pinch of cayenne pepper for some spice.
  • Try different herbs, such as fresh thyme or torn basil leaves.
  • This combination of ingredients works amazing as a vegetarian quesadilla too. Just tuck the mushroom mixture and cheese into a flour tortilla instead of between bread.
  • Instead of cooking the sandwich in butter, spread some mayo on the outsides before assembling and use the fat from the mayo for cooking.
  • Prep ahead: You can sauté the onions and mushrooms in advance and just keep the mixture in the fridge for up to 3-4 days. Assemble and enjoy this sandwich in about 5 minutes! The only thing is that the cheese will take longer to melt since you'll be placing it on cold mushrooms. You can either heat up the mushroom mixture a little before assembling your sandwich, or cover your pan with a lid to keep the heat in and help the cheese melt.

More mushroom recipes to try: Sauteed Potatoes with Mushrooms

If you enjoyed this recipe, let me know with a comment and a star rating below. And don't forget to share it on Facebook and save it on Pinterest for later!

Two mushroom grilled cheese sandwiches stacked on top of each other
Print Recipe
5 from 1 vote

Mushroom Onion Grilled Cheese

This easy lunch sandwich is melty, cheesy, gooey, with a wonderful earthy umami flavor thanks to sauteed mushrooms and onions. Read the notes below the recipe for make-ahead tips and recipe variations!
Prep Time10 minutes
Cook Time40 minutes
Total Time50 minutes
Course: Lunch, Main Course
Cuisine: American
Diet: Vegetarian
Servings: 2 sandwiches
Author: Kate

Ingredients

  • 3 cups baby bella mushrooms - cleaned and sliced (about a 10-16 oz package)
  • 1 yellow onion - thinly sliced into half moons
  • 1 teaspoon salt - divided, or to taste
  • ¼ - ½ teaspoon ground black pepper - to taste
  • 3 tablespoons butter - divide (or use olive oil)
  • 2 tablespoons fresh parsley leaves - finely minced
  • 4 slices bread - (sliced white bread, such as brioche, sourdough, or Texas toast, but whole wheat is also a great option!)
  • 2-4 slices mozzarella cheese - (or use any combination of mozzarella, provolone, white cheddar, gouda... or try smoked versions of each of these cheeses!)

Special equipment

  • 1-2 Skillets (1 large or 2 smaller)
  • Bowl
  • Tongs and wet paper towel to clean out the pan

Instructions

  • Heat a large pan over medium heat. Add 2 tablespoons of butter (or olive oil), sliced onion, half the salt, and pepper. Sauté for about 20 minutes and let the onions caramelize without burning. If needed add a few tablespoons of water to prevent burning.
  • Remove the onions to a bowl, and add the mushrooms and the rest of the salt. Turn up the heat and cook over medium-high heat for 5-7 minutes or until cooked down to your liking, stirring constantly.
  • Add the mushrooms to the bowl with the onions. Add the parsley, and stir everything together.
  • Assemble your sandwiches: place 1 slice of cheese on your bread. Top with half the mushroom mixture. If using more cheese, top the mushroom mixture with another slice, and top with the other bread.
  • Use tongs and a damp paper towel to wipe down the skillet. Melt the butter in the pan and cook the sandwiches until the bread is golden brown and the cheese is melted.

Notes

  • If cooking both sandwiches in 1 large pan, melt about ½ tablespoon of butter in the pan, cook on one side, then add the rest of the butter and cook on the other side. If using two smaller pans, use about ¼ tablespoon butter for each side of the sandwich.
  • Try a pinch of cayenne pepper for some spice, or different herbs, such as fresh thyme or torn basil leaves.
  • This mushroom + onion combination works great as a quesadilla too. 
  • Instead of cooking the sandwich in butter, spread some mayo on the outsides before assembling and use the fat from the mayo for cooking.
  • Prep ahead: You can sauté the onions and mushrooms in advance and just keep the mixture in the fridge for up to 3-4 days. The only thing is that the cheese will take longer to melt. You can heat up the mushroom mixture before assembling your sandwich or cover your pan with a lid to keep the heat in.

Nutrition

Calories: 479kcal (24%) | Carbohydrates: 38g (13%) | Protein: 19g (38%) | Fat: 29g (45%) | Saturated Fat: 17g (85%) | Polyunsaturated Fat: 2g | Monounsaturated Fat: 8g | Trans Fat: 1g | Cholesterol: 79mg (26%) | Sodium: 1840mg (77%) | Potassium: 706mg (20%) | Fiber: 4g (16%) | Sugar: 8g (9%) | Vitamin A: 1153IU (23%) | Vitamin C: 10mg (12%) | Calcium: 329mg (33%) | Iron: 3mg (17%)

The nutritional information displayed is an estimate and not to be used as dietary or nutritional advice. Consult a nutritionist or dietician for nutritional info based on the exact ingredients you use.

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