Preheat your oven to 400°F (200°C).
Lightly grease a baking dish and place the tilapia fillets in a single layer.
In a microwave-safe bowl, combine the butter, minced garlic, chopped parsley, red pepper flakes, juice of one lemon, and a pinch of salt and pepper. Microwave for about 30 seconds until melted.
Drizzle the lemon butter sauce over the tilapia fillets, ensuring they are well-coated.
Thinly slice the remaining lemon and place the slices on top of the fillets.
Bake the tilapia for 15-20 minutes, or until it flakes easily with a fork.
Remove from oven, garnish with extra parsley, and serve immediately.