Preheat the oven to 400 degrees F (204 degrees C)
Use paper towels to pat the fish fillets dry. Arrange them in a single layer in a 9×13 baking dish. Cut the lemon in half. Juice and zest one half (you should get about 1 tablespoon lemon juice and 1/2 tablespoon lemon zest). Slice the other half into thin slices.
In a small bowl in the microwave or saucepan on the stove, melt the butter. Remove from heat. Stir in the lemon juice, lemon zest, parsley, and crushed garlic. Brush the garlic lemon butter over the tilapia fillets. Season with sea salt and black pepper. Flip and repeat both lemon butter and seasoning on the other side. Arrange the lemon slices over the fish.
Bake for 12-15 minutes, (will vary by thickness), until the baked tilapia is opaque and flakes easily with a fork.
