Set an oven rack about 6 inches from the heat source and preheat the oven's broiler. Grease a rimmed baking sheet; place halibut fillets on the sheet.

Broil in the preheated oven until fish flakes easily with a fork, about 8 minutes.

Meanwhile, mix Parmesan cheese, butter, mayonnaise, green onions, lemon juice, salt, and hot pepper sauce in a bowl.

Remove fillets from the oven; spread Parmesan mixture over top. Return to the oven and broil until topping is bubbly and lightly browned, about 2 more minutes.

Serve hot and enjoy!