Slice the beef thinly.
Cut the onion, bell pepper, and mushrooms into bite-sized pieces.
Marinate the beef with soy sauce, sugar, minced garlic, and pepper to make bulgogi seasoning.
Add cooking oil to a pan and stir-fry the marinated beef.
Add the prepared vegetables and stir-fry together.
Boil the pasta noodles and drain them.
Add the noodles to the stir-fried bulgogi and vegetables, then mix well.
Taste and adjust with salt and pepper to finish.
Plate and garnish with parsley.