Set an oven rack about 6 inches from the heat source and preheat the oven's broiler. Lightly grease a baking pan.

Place grouper fillets on the prepared baking pan; brush with lemon juice. Combine Parmesan cheese, butter, mayonnaise, hot pepper sauce, salt, and pepper in a small bowl; set aside.

Broil fillets in preheated oven until fish flakes easily with a fork, about 4 to 6 minutes; remove the pan from the oven and spread cheese mixture on top of fillets.

Return to the broiler for an additional 30 seconds, or until topping is browned and bubbly.