Wash and julienne the bean sprouts, onion, carrot, and bell pepper.
Boil japchae glass noodles in boiling water for 5 minutes, then rinse with cold water.
Heat cooking oil in a pan and sauté minced garlic.
Add the onion, carrot, and bell pepper, and stir-fry. Then add bean sprouts and stir-fry once more.
Add the boiled glass noodles to the pan and mix well.
Add gochujang (Korean red chili paste), soy sauce, red pepper powder, sugar, and sesame oil. Stir-fry quickly so the seasoning gets absorbed.
Sprinkle with black pepper and sesame seeds to finish.