Cut the pork neck into bite-sized pieces.
Slice the aged kimchi into appropriate lengths.
Julienne the onion and green onion.
In a bowl, mix together chili powder, soy sauce, sugar, minced garlic, black pepper, and sesame oil to make the sauce.
Add the pork neck, aged kimchi, and onion to a pan and stir-fry over medium heat.
Add the sauce and continue stir-frying until the ingredients are cooked through.
Add the green onion and stir-fry a bit more.