Boil the somyeon (thin wheat noodles), rinse under cold water, and drain well.
Slice onion and scallion thinly.
In a bowl, mix soy sauce, sugar, vinegar, minced garlic, sesame oil, and water to make the sauce.
Pour the sauce over the cooked noodles and mix well.
Top with the sliced vegetables and garnishes such as egg strips or seaweed flakes.