Cut the beef round and vegetables (onion, carrot, bell pepper, green onion) into bite-sized pieces.
Heat cooking oil in a pan and stir-fry the beef round over high heat.
When the meat is about halfway cooked, add the chopped vegetables and continue stir-frying.
Add soy sauce, minced garlic, black pepper, and sugar, then stir-fry quickly.
When the vegetables are slightly wilted, finish by drizzling sesame oil.