Slice the round beef thinly into bite-sized pieces.
Julienne the onion, carrot, and green onion.
Prepare the marinade with soy sauce, sugar, minced garlic, sesame oil, and black pepper.
Add the sliced beef and vegetables to the marinade and let them sit for 20 minutes.
Heat cooking oil in a pan and add the marinated meat and vegetables.
Stir-fry over medium heat until the beef is cooked through.
Sprinkle sesame seeds on top to finish.