Clean and prepare the boneless cutlassfish fillets.
Slice the radish and onion thickly.
Layer the radish and onion at the bottom of a pot.
Place the prepared cutlassfish fillets on top.
Mix gochujang, soy sauce, minced garlic, red pepper powder, sugar, pepper, and water to make the sauce.
Pour the sauce over the ingredients.
Simmer over medium heat until the broth thickens.
Add Cheongyang chili pepper and green onion, cook for 5 more minutes to finish.