Preheat your oven broiler. Line a broiling pan or baking sheet with aluminum foil and grease it lightly to prevent sticking.
In a small bowl, combine the Parmesan cheese, softened butter, mayonnaise, and lemon juice.
Add the dried basil, black pepper, onion powder, and celery salt to the bowl. Mix everything together until you have a smooth paste and set it aside.
Arrange the tilapia fillets in a single layer on the prepared pan. If desired, lightly sprinkle them with salt, pepper, and a pinch of Cajun seasoning.
Place the pan in the oven a few inches from the heat source. Broil for 2 to 3 minutes.
Carefully flip the fillets over and broil for another 2 minutes.
Remove the pan from the oven. Spread the Parmesan cheese mixture evenly over the top side of each fillet.
Return the fish to the broiler for an additional 2 to 3 minutes, or until the topping is golden brown and bubbly and the fish flakes easily with a fork.
Serve immediately with fresh lemon wedges.