Cut the Korean radish into pieces approximately 0.5 inches thick. Slice the black cod into pieces about 0.5 inches thick.
2
Place the black cod and radish in a pot, add 2 cups of water. Cover and cook over medium-high heat for 15 minutes.
3
Make the braising sauce by mincing 6 cloves of garlic and placing them in a bowl. Add 1 tablespoon gochugaru, 1 teaspoon sugar, 1/3 cup soy sauce, and 1/2 teaspoon cooking oil. Mix well.
4
Cut the onion, green chili pepper, and green onion into coarse pieces.
5
After 15 minutes, uncover the pot. Add the onion and green chili pepper first, then the green onion. Add the black cod and pour in the sauce. Cover and cook over medium heat for 10 minutes.
6
After 10 minutes, gently move the radish around to ensure even cooking. Scoop some of the braising liquid and pour it over the fish. Cook for another 5 minutes.
7
Continue cooking over medium heat for another 2–3 minutes until all the flavors are well incorporated. The fish should be very flaky and the radish should be tender.