Combine sugar, red pepper flakes, gochujang, cooking wine, soy sauce, and minced garlic in a bowl to make the seasoning.

Chop the onion and green onion into small pieces.

Slice the pork belly into bite-sized pieces.

Combine the pork belly, chopped onions, and seasoning in a bowl.

Cover the bowl with plastic wrap and let it marinate at room temperature for 20–30 minutes.

Heat a frying pan over low heat and add a small amount of cooking oil. Add the marinated pork belly and cook on low heat initially.

Once the pork starts releasing juices, increase the heat to medium and continue cooking.

Slice the green chilies diagonally and add them to the pan. Cook until the pork is fully cooked.