Cut the beef and enoki mushrooms into bite-sized pieces.
Slice vegetables such as onion and green onion.
In a bowl, make the marinade with soy sauce, sugar, minced garlic, and pepper.
Marinate the beef in the sauce for 10 minutes.
Heat cooking oil in a pan, then add the marinated beef, vegetables, and enoki mushrooms; stir-fry.
Once the ingredients are cooked, plate and serve.