Preheat the oven to 400 F. Season tilapia with salt and pepper and place in a 13x9 baking pan or a pan large enough to hold the filets in a single layer.
In the microwave or in a small pot, melt the butter until it turns a light golden brown. In a small bowl or pitcher, mix together the melted butter, Parmesan, garlic, red pepper flakes, lemon juice, and zest, then pour over the fish.
Bake the tilapia for 10 to 12 minutes or until the fish is cooked through (flaky and opaque). Transfer to plates or a serving platter and sprinkle with the parsley; serve hot.
Notes
The butter sauce cooks along with the fish resulting in a browned butter sauce that is fragrant with garlic and brightened by the lemon juice and lemon zest. If you like a spicier sauce, add a bit more red pepper flakes. Make sure to serve some nice crusty bread with the fish to sop up all of the delicious sauce. Or serve the fish with its sauce over rice or another starch or grain like polenta or grits so that not a drop gets wasted.