Preheat the oven to 425°F. and spray a baking pan with nonstick spray.
Combine the bread and lemon zest in a food processor; pulse to form coarse crumbs.
In a small bowl, mix together the mustard and lemon juice.
Sprinkle both sides of the fillets with salt and pepper and place them in the pan. Brush with the mustard mixture and then top with the bread crumbs, pressing down so that the crumbs adhere. Spray lightly with nonstick spray.
Bake until the coating is golden and the fish is just opaque in the center, about 8 minutes. Serve with lemon wedges, if desired.
Notes
You may also substitute flounder, red snapper, catfish, cod or any other white fish.