Cut the pork neck into bite-sized pieces.
Slice the onion, green onion, and chili pepper.
In a bowl, mix red pepper powder, gochujang (Korean chili paste), soy sauce, minced garlic, sugar, black pepper, and sesame oil to make the marinade.
Marinate the pork neck and vegetables in the sauce for 10 minutes.
Add cooking oil to a pan and preheat over medium heat.
Add the marinated pork neck and vegetables to the pan and stir-fry.
Stir-fry over medium heat for 8–10 minutes until the meat is cooked through.
Finish by sprinkling sesame seeds on top.