Slice the cucumbers thinly, about 1/8-inch thick. For best results, use a mandoline slicer if available. Place them in a large bowl.
Add the sliced red chili to the cucumbers.
In a small bowl, whisk together rice vinegar, soy sauce, sesame oil, sugar, and salt until the sugar and salt are completely dissolved.
Pour the dressing over the cucumbers and chili, then toss gently to ensure every slice is coated.
Let the salad rest for at least 10 minutes, but preferably 30 minutes if you have time, to allow the flavors to meld.
Just before serving, give the salad another gentle toss to redistribute the dressing.
Sprinkle sesame seeds and chopped cilantro on top for garnish and added flavor.
Taste and adjust seasoning if needed before serving.
