Set an oven rack about 4 inches from the heat source and preheat the oven’s broiler. Line a broiler pan with aluminum foil.

Mix Parmesan cheese, butter, mayonnaise, lemon juice, basil, pepper, onion powder, and celery salt together in a bowl until well combined.

Arrange tilapia fillets in a single layer on the prepared pan.

Broil in the preheated oven for 4 minutes, flipping halfway through. Remove from the oven and spread Parmesan mixture over fillets. Return to the oven and broil until topping is browned and fish flakes easily with a fork, about 2 more minutes; be careful not to overcook.