Cut the pork and mushrooms into bite-sized pieces.
Combine gochujang, soy sauce, minced garlic, chili powder, sugar, and sesame oil in a bowl to make the marinade.
Add the marinade to the pork and let it sit for 10 minutes.
Heat cooking oil in a pan and stir-fry the pork.
When the pork is half cooked, add mushrooms and onion and stir-fry together.
When all ingredients are fully cooked, transfer to a plate and serve.