Cut the beef into bite-sized pieces.
Slice the onion thinly.
Heat oil in a pan and sauté the onion.
Add the beef and stir-fry.
Season with soy sauce, sugar, and cooking wine.
Stir-fry until the ingredients are cooked through.
Place the cooked beef and onions over rice.
Finish by sprinkling chopped green onions as desired.