Peel the cucumbers if desired, then place them on a cutting board and slice as thin as possible using a sharp knife or mandoline. You should hear a crisp sound with each stroke, and the seeds will be visible as a mess of juice and flesh.
Transfer the cucumber slices directly into a mixing bowl, feeling the crunch and coolness as you drop them in. The slices should be almost paper-thin and slightly translucent.
In a small bowl, whisk together rice vinegar, salt, sugar, and chili flakes until the salt and sugar dissolve completely. This creates a bright, tangy dressing.
Pour the vinegar dressing over the cucumber slices, then toss everything gently with your hands or a spoon. You'll hear the crunch as the slices absorb the tangy liquid and start to soften slightly.
If using, sprinkle chopped herbs over the salad for an extra burst of freshness and flavor. Give it a final toss to evenly distribute.
Serve immediately for maximum crunch, or chill in the fridge for up to a few hours to allow flavors to meld. The salad should be crisp, tangy, and refreshingly cool, perfect as a light side.
