Gather all the ingredients.
Cut ½ lb kimchi into smaller pieces with a knife or a pair of scissors.
Cut ½ onion into slices ¼ inch (6.3 mm) thick.
Cut 2 green onions/scallions into 2-inch (5-cm) pieces. If the white parts are too thick, cut them in half lengthwise.
Cut ½ lb thinly-sliced pork belly into 2-inch (5-cm) pieces.
Season the pork belly slices with ⅛ tsp Diamond Crystal kosher salt and ⅛ tsp freshly ground black pepper.
Preheat a large frying pan over medium-high heat. When the pan is hot, add 1 Tbsp neutral oil, spread it evenly, and then add the pork belly slices.
Stir-fry the pork with a blunt-end wooden spatula until it is no longer pink. If your pork belly has rendered too much fat, you can wipe off the excess oil in the pan with a paper towel.
Add the onion slices and green onions to the pan.
Stir-fry until the onions are slightly tender, about 2–3 minutes. Then, add 1 Tbsp sake and mix well.
Add the kimchi and stir to mix with the rest of the ingredients.
Add 1 Tbsp kimchi juice and 2 tsp soy sauce. Stir-fry until there is no liquid left in the pan, about 1 minute.
Drizzle 1 tsp toasted sesame oil on top and mix it all together. Transfer the stir-fry to a serving plate or individual plates. Serve hot with steamed rice.
