Slice the beef thinly.
Julienne the onion, carrot, and green onion.
Mix soy sauce, sugar, minced garlic, sesame oil, and pepper to make the marinade and toss the beef in it.
Heat cooking oil in a pan and add the marinated beef and vegetables.
Stir-fry over medium heat until the ingredients are cooked through.
Sprinkle with sesame seeds to finish.