Cut the thinly sliced pork belly and vegetables into bite-sized pieces.
Make the sauce by mixing gochujang (Korean chili paste), red pepper flakes, soy sauce, minced garlic, sugar, pepper, and sesame oil.
In a bowl, mix the pork belly, sauce, and vegetables together.
Heat oil in a pan and stir-fry the ingredients over high heat.
When the meat is cooked and the vegetables are slightly softened, turn off the heat.
Finish by sprinkling chopped green onions and sesame seeds, if desired.