Cut the pork into bite-sized pieces.
Thinly slice the onion, green onion, and chili pepper.
Make the marinade by mixing gochujang (Korean red chili paste), red pepper powder, soy sauce, minced garlic, sugar, and black pepper.
Add the marinade to the pork and mix well, then let it sit to marinate.
Heat oil in a pan and stir-fry the green onion to release its aroma.
Add the pork and stir-fry over high heat.
Add the onion and chili pepper and stir-fry further.
When everything is cooked through, turn off the heat.