Cook the buckwheat noodles in boiling water, then rinse them in cold water.
Cut cucumber, carrot, onion, and bell pepper into thin strips.
In a bowl, mix gochujang (Korean chili paste), soy sauce, vinegar, sugar, sesame oil, and minced garlic to make the sauce.
Place the noodles and vegetables in a bowl, add the sauce, and mix well.
Sprinkle chili powder and sesame seeds to taste to finish.