Boil the buckwheat noodles in boiling water and rinse them in cold water.
Drain the noodles using a strainer to remove excess water.
Place the noodles in a bowl and drizzle with perilla oil.
Mix soy sauce, vinegar, and sugar to make the sauce.
Top the noodles with cucumber, seaweed flakes, green onion, sesame seeds, and other garnishes.
Serve with the sauce on the side.