Preheat the oven to 425°F (220°C).
Line a sheet pan with parchment paper or lightly grease it with olive oil to prevent sticking.
Pat the tilapia fillets completely dry with paper towels. Dry fish browns better and helps the coating adhere.
In a small bowl, mix mayonnaise and lemon juice. Brush a thin layer over the top of each fillet. Season the fish with salt and pepper.
In another bowl, combine Parmesan, garlic powder, paprika, onion powder, and red pepper flakes if using.
Drizzle the sheet pan with olive oil or melted butter.
Place the fillets on the pan, mayo-side up.
Press the Parmesan mixture evenly over the tops of the fillets, covering fully. Press gently so it adheres.
Bake for 10–12 minutes, depending on thickness. The fish should flake easily with a fork.
For extra color, switch to broil for 1–2 minutes at the end. Watch closely so the cheese doesn’t burn.
Finish with a squeeze of lemon and a sprinkle of fresh parsley or chives.
Serve hot.