Cut the onion and pork shoulder into bite-sized pieces.
Make the marinade with soy sauce, minced garlic, sugar, black pepper, and sesame oil, then mix with the meat and onion. Marinate for 20 minutes.
Heat cooking oil in a pan over medium heat, add the onion and pork shoulder, and stir-fry.
Continue to stir-fry until the pork is cooked and the onions become translucent.
Transfer the cooked pork shoulder stir-fry to a plate and serve.