Drain the sea snails (golbangyi) and reserve 1 tablespoon of juice. Rinse the sea snails and cut in half if the pieces are too big.
In a large mixing bowl, combine cabbage, onion, carrots, cucumber, and the sea snail. Set aside.
In a small mixing bowl, combine garlic, chili paste, chili flakes, vinegar, sugar, plum extract (if you don't it, add reserved sea snail juice), and sesame seeds. Mix them well to make the sauce.
Drizzle the sauce over to the sea snail and vegetable mixture and toss well. Chill in the fridge while you are getting the noodles ready.
Cook the noodles in a package direction or boil in the water for 3-4 minutes. Rinse the noodles in the cold running water and drain well.
Place sea snail salad with cold wheat noodles on the side. Garnish with green onion. Toss well before you serve.