Cut the aged kimchi, pork neck, and onion into bite-sized pieces.
Add cooking oil to the pan and stir-fry the pork.
When the pork is halfway cooked, add the onion and aged kimchi and stir-fry together.
Season with gochujang, soy sauce, minced garlic, red pepper powder, and a bit of sugar.
Stir-fry until all the ingredients are well mixed, then add sesame oil and green onion and sauté once more.
Transfer to a plate and serve.