Preheat and prep: Heat the oven to 425°F (220°C). Line a sheet pan with parchment and lightly oil it so the skin releases easily.
Dry the salmon: Pat salmon dry with paper towels.
This helps the crust stick and promotes even cooking. Place skin-side down on the pan.
Season the fish: Sprinkle salmon with 1/2 teaspoon salt and 1/4 teaspoon pepper total. Zest half the lemon over the fillets.
Make the crust: In a bowl, mix Parmesan, panko, garlic, parsley, lemon zest (the rest), a pinch of red pepper flakes, 2 tablespoons olive oil, and melted butter if using.
It should feel like damp sand that clumps when pressed.
Add a flavor base: Brush the top of each fillet with Dijon mustard (about 1/2 teaspoon each). This helps the crust adhere and adds tang.
Press on the topping: Divide the crumb mixture over the salmon and press gently to form an even layer, edge to edge.
Bake: Cook for 12–15 minutes for 1-inch-thick fillets, or 15–18 minutes for a whole side. The topping should be golden and the salmon should flake easily with a fork.
Optional broil: For extra crunch, broil for 1–2 minutes at the end.
Watch closely to avoid burning.
Rest and serve: Let sit 2 minutes. Squeeze fresh lemon over the top and serve with more wedges.