Wash the bean sprouts thoroughly and set aside.
Cut the thinly sliced pork belly into bite-sized pieces.
Julienne the onion and green onion.
Stir-fry the pork belly in a pan first.
When the meat is halfway cooked, add the onion, green onion, and bean sprouts.
Season with gochujang, soy sauce, minced garlic, sugar, and pepper.
Stir-fry over high heat until all ingredients are cooked through.
Serve on a plate.