2tablespoonscrumbled feta(or queso fresco or cojita cheese)
Season the shrimp with the taco seasoning. Heat the olive oil in a large pan, and cook the shrimp about 2-3 minutes per side over high heat, or until fully cooked. Set aside.
Mash the avocado in a small bowl and mix with the lime juice.
To arrange the tostadas, spread 1/4 of the avocado onto each tostada, and season with a pinch of salt & pepper. Top each tostada with 3-4 shrimp, halved tomatoes, diced bell peppers, diced scallions, and feta cheese. Squeeze extra lime juice over the tostadas, if desired. Serve immediately.
These are best eaten fresh. If you are not going to eat all 4 right away, just prep all the ingredients and keep them refrigerated (except for the tostada shells). Assemble the rest of the tostadas right when you're ready to eat.