Rinse 4 medium cucumbers under cold water and, if desired, peel them. Slice thinly, about 1/8-inch thick, and place in a large mixing bowl.

In another bowl, whisk together rice vinegar, soy sauce, sesame oil, and sugar until dissolved. Optionally, add minced garlic.

Add sliced red onion to the cucumbers. Pour the dressing over, tossing gently until everything is well-coated.

Let the salad chill in the refrigerator for at least 10 minutes for the flavors to meld.

Before serving, sprinkle with chopped fresh cilantro or mint and sesame seeds or chopped peanuts.