Soak glass noodles in hot water.
Slice beef and vegetables (onion, carrot, bell pepper, etc.) thinly.
Add cooking oil to a pan and stir-fry the beef.
Add the vegetables and stir-fry together.
Add the soaked glass noodles and season with soy sauce, sugar, and sesame oil.
Mix well and stir-fry evenly.
Serve the japchae over rice to finish.