Preheat your oven to 400°F (200°C). This ensures that your tilapia cooks evenly and develops a lovely golden crust.
In a mixing bowl, combine the softened butter, mayonnaise, lemon juice, Parmesan cheese, dried parsley, ground black pepper, garlic salt, onion powder, and celery salt. Mix until everything is well blended and creamy.
Place the tilapia fillets in a baking dish. Make sure they are arranged in a single layer for even cooking. You can lightly season them with a pinch of salt and pepper if desired.
Using a spoon or spatula, spread the creamy Parmesan mixture generously over each fillet. Make sure to cover the fish completely to lock in moisture and flavor.
Put the baking dish in the preheated oven and bake for about 15-20 minutes, or until the tilapia is cooked through and flakes easily with a fork. The topping should be golden and bubbly.
Once done, remove the dish from the oven and let it cool for a couple of minutes. Serve the Baked Tilapia Parmesan hot, garnished with additional parsley or lemon wedges if desired.