Finely chop the green onion and garlic.
In a large bowl, combine all the sauce ingredients and mix well to make the seasoning sauce.
Cook the buckwheat noodles according to the package instructions, then rinse them several times under cold water to wash off the starch and drain thoroughly.
Add the noodles to the sauce and toss until evenly coated, then finish with the perilla oil and mix gently once more. Plate the noodles and top with as much seaweed as you like.
Tip.Adjust the seasoning to your taste. For a sweeter version, add more sugar or maesil-cheong, and for extra heat, increase the gochugaru. Add the perilla oil at the very end so its aroma stays fresh.