Preheat the oven to 350 degrees F (175 degrees C).
In a small bowl, mix together the onion and mustard. Season the catfish fillets with garlic salt and pepper. Place on a baking tray and coat with the onion and honey. Sprinkle parsley flakes over the top.
Bake for 20 minutes in the preheated oven, then turn the oven to broil. Broil until golden, 3 to 5 minutes.