Preheat oven to 400F. Spray or brush a large baking sheet with oil, or line a baking sheet with parchment paper and then spray it with oil.
In a large dinner plate, combine the ⅓ cup panko breadcrumbs, ⅓ cup grated Parmesan, and 1 teaspoon herbs de Provence. Mix to combine.
In a small bowl, combine the 1.5 tablespoon Dijon mustard and 1.5 tablespoon mayonnaise and mix well.
Season the perch with salt and pepperon both sides. Lay flat (skin side down if the skin is on). Use the back of a spoon to spread the mayo+mustard mixture on top of the perch fillets (top side only).
Use your hands to place the perch fillets mustard side down into the breadcrumbs mixture. Press down gently but firmly to get the breadcrumbs to coat the bottom. You're coating just one side.
Arrange the breaded perch fillets on the baking sheet with the breadcrumb side up. Spray the tops with olive oil.
Bake in a preheated oven for 5-6 minutes. Turn on the broiler and broil for 2-3 minutes, or until the breadcrumbs are golden brown and the perch is cooked through. Keep a close eye on the tops of the perch to make sure the breadcrumbs don't burn!
Serve warm, squeezing fresh lemon juice over the tops of the perch fillets.
Notes
The nutrition facts are estimated assuming 1 lb of perch for 4 people, which ends up being 2-3 pieces per person, depending on the size of the fillets.