Wash the cucumber and tomato thoroughly, then slice them thinly into strips.
Slice the onion and green onion into thin strips as well.
Boil the somyeon noodles in boiling water, rinse with cold water, and drain well.
Make the bibim sauce by mixing gochujang (Korean red chili paste), soy sauce, vinegar, sugar, minced garlic, and sesame oil.
Place the sliced cucumber, tomato, onion, and green onion on the cooked noodles, add the bibim sauce, and mix well.
Sprinkle sesame seeds on top if desired to finish.