Wash the bean sprouts and beef thoroughly and cut them into bite-sized pieces.
Thinly slice the onion and green onion.
In a bowl, marinate the beef with soy sauce, minced garlic, sugar, pepper, and sesame oil.
Heat oil in a pan and stir-fry the onion and green onion.
Add the marinated beef and stir-fry, then place the bean sprouts on top.
Cover with a lid and cook on low heat for 3-5 minutes.
Finish by drizzling sesame oil and sprinkling sesame seeds on top.