Take each catfish fillet and brush the mustard-mayo mixture on both sides.
In a separate shallow dish, add 1 cup of your favorite premade fish fry. I used Louisiana Fish Fry. Store bought fish fry is loaded with salt and seasonings, this is where all the seasoning comes from. If you feel you need more seasoning, lightly season the fish filet with garlic powder, lemon pepper, and Creole seasoning before coating in the fish fry.
Lay one of the mustard-mayo-coated catfish fillets in the fish fry mixture, ensuring it's evenly coated on both sides. Gently press the coating onto the fillet to make it stick.
Repeat this process with the remaining catfish fillets.