Slice the pork thinly.
Julienne the onion, Fuji apple, and green onion.
In a bowl, mix gochujang, soy sauce, sugar, minced garlic, red pepper powder, and grated Fuji apple to make the marinade.
Combine the pork with the marinade and let it marinate for 20 minutes.
Heat oil in a pan and stir-fry the pork.
Add the onion and green onion and stir-fry together.
Once the ingredients are cooked, plate and serve.