Cut the pork into bite-sized pieces and slice the onion and green onion.
In a bowl, mix gochujang (Korean red chili paste), soy sauce, sugar, minced garlic, red pepper powder, and sesame oil to make the marinade.
Add the marinade to the pork and let it marinate for 10 minutes.
Heat oil in a pan and stir-fry the green onion to make green onion oil.
Add the onion and the marinated pork to the pan and stir-fry.
Cook over medium heat until the pork is fully cooked.
Serve the stir-fried pork over rice to finish.