Line a baking sheet with foil and lightly coat with oil or cooking spray. Place tilapia on the sheet and brush with the melted butter. Season with salt and pepper. Place the fish in the oven on the top rack, positioned a few inches below the broiler element. Broil on high for 10-15 minutes until light golden brown and easily flaked with a fork. Spritz with lemon juice and garnish with lemon slice. Serve with your favorite sauce.