Cut the chicken breast into bite-sized pieces.
Julienne the onion, carrot, and bell pepper.
Soak the cup noodle japchae noodles in hot water.
Heat cooking oil in a pan and stir-fry the chicken breast.
Add the vegetables and stir-fry together.
Add the soaked japchae noodles and seasonings (soy sauce, sugar, sesame oil, pepper) and stir-fry.
Serve the cooked japchae over rice.