Cut the thinly sliced pork belly into bite-sized pieces.
Slice the onion, green onion, and Cheongyang chili pepper.
In a bowl, mix gochujang, soy sauce, sugar, minced garlic, and gochugaru to make the sauce.
Add the sauce to the pork belly and mix well by hand.
Heat cooking oil in a pan and stir-fry the green onion to bring out the aroma.
Add the marinated pork belly and vegetables to the pan, and stir-fry over high heat.
Stir-fry until the meat is fully cooked, then add the Cheongyang chili pepper at the end and mix well.
Transfer to a plate to serve.