Preheat oven to 400℉ (204℃) and lightly grease a 9x13-inch baking dish with nonstick cooking spray.
Lay 4 (6 ounce) tilapia filets into the prepared baking dish.
In a small bowl, whisk together 3 tablespoons lemon juice, 2 tablespoons salted butter (melted), and 1 tablespoon minced garlic. Pour over tilapia. Season with 1/2 teaspoon salt and 1/2 teaspoon black pepper. Tuck lemon slices in to surround and top the fish.
Bake for 10-12 minutes or until fish flakes easily with a fork.
Serve hot and garnish with 2 tablespoons chopped fresh parsley.