1 small English cucumber, peeled, seeded and cut into matchsticks (about 1 1/4 cups)
1/4 mild onion, such as Vidalia or Sweet D (optional), cut vertically into thin half moons
3 tablespoons plus 2 tablespoons unseasoned rice vinegar
3 tablespoons Korean or Japanese soy sauce
1 tablespoon organic cane sugar, or 2 1/2 teaspoon regular white sugar
3 or 4 cloves garlic, minced or crushed with a garlic press
1 to 1 1/2 teaspoons Korean red pepper powder (gochugaru)
1/2 to teaspoon MSG salt or kosher salt
Toasted sesame seeds, for garnish
In a pot or glass or plastic storage container, soak the dried wakame and kombu in the water for about 2 hours, or cover and refrigerate overnight.
Remove and discard the kombu. Strain the soup into a bowl to reserve the liquid, keeping it in the fridge. Transfer the wakame to a bowl. Add the cucumber, onion (if using), rice vinegar soy sauce, garlic and Korean red pepper powder. Stir and marinate for about 30 minutes.
Add the seasoned vegetables to the reserved soaking liquid. Add the remaining 2 tablespoons rice vinegar, then season with the salt of your choice. Serve in individual bowls, garnished with a sprinkling of sesame seed. Invite guests to add ice cubes as needed to ensure that the soup remains cold.