Cut the pork into bite-sized pieces.
Chop the onion, green onion, and garlic.
Mix gochujang, soy sauce, sugar, minced garlic, red pepper powder, and sesame oil to make the marinade.
Put the pork, vegetables, and marinade into a bowl, mix well, and let it marinate for 20 minutes.
Heat cooking oil in a pan and stir-fry the marinated pork over medium heat.
When the pork is cooked, add the green onion and quickly stir-fry to finish.