Cut the beef and vegetables into bite-sized pieces.
Add oil to a pan and stir-fry the beef.
Add onions, bell peppers, and other vegetables, and sauté together.
Season with soy sauce, sugar, garlic, and sesame oil.
Add the cooked pasta noodles and stir-fry everything together to combine the flavors.
Transfer to a plate and sprinkle with sesame seeds to finish.