Soak dangmyeon (glass noodles) in water for 10 minutes.
Julienne the beef, onion, carrot, and bell pepper.
Add cooking oil to a pan and stir-fry the beef.
Add the onion, carrot, and bell pepper, and stir-fry together.
Add the soaked dangmyeon, season with soy sauce, sugar, and sesame oil.
Mix all the ingredients well and stir-fry.
Serve japchae on top of rice to finish.