Clean the catfish, remove the skin, and debone it. Marinate the fish with 2 tablespoons soy sauce, 2 tablespoons teriyaki sauce, and 1 tablespoon sugar mixed with 1 tablespoon cooking oil. Pour the mixture evenly over the fish and rub it in with your hands. Slice onion, garlic, and chili pepper, and add them along with black pepper. Let the fish marinate for 20 minutes.

After marinating, place the fish in the oven at 320°F (160°C) for the first 15 minutes. Take it out, flip the fish, and bake for another 15 minutes. Turn off the oven, add chopped green onions on top, and leave it in the oven until ready to serve. Reheat at a lower temperature if needed before eating.