Wash the mackerel, cut it into pieces, and marinate with salt and rice wine for 10 minutes to remove fishy smell.
Slice the radish into 1cm thick pieces and julienne the onion.
Layer the radish at the bottom of a pot, then add the mackerel and onion on top.
Make the sauce by mixing gochujang (red chili paste), soy sauce, chili powder, minced garlic, sugar, rice wine, and water.
Pour the sauce over the ingredients and boil over high heat.
Once boiling, reduce to medium-low heat and simmer for 20 minutes until the sauce thickens.
Add chopped green onion and Cheongyang chili peppers, and simmer for 5 more minutes.