Cut the Persian cucumbers into rounds approximately 1/4 inch (6 mm) thick. Keep the slices as even as possible so they soften and absorb the dressing at the same rate.

Place the sliced cucumbers in a large colander set over a bowl or sink. Sprinkle with the salt and toss thoroughly. Let them stand for 20 minutes. Moisture should begin collecting beneath the colander.

While the cucumbers drain, whisk together the rice vinegar, soy sauce, toasted sesame oil, sugar, garlic, chili crisp, and optional red pepper flakes in a small bowl. Continue whisking until most of the sugar dissolves.

Shake the colander well to remove released liquid: Spread the cucumbers on a clean kitchen towel or several layers of paper towels and blot gently. They should feel cool and slightly flexible but not wet.

Transfer the dried cucumbers to a large mixing bowl. Pour the dressing over them and toss until every slice looks lightly coated.

Add the sliced green onions, toasted sesame seeds, and cilantro, if using. Toss gently so the onions and sesame seeds are distributed without breaking the cucumber slices.

Let the salad stand for 5 minutes before serving. This gives the cucumbers time to absorb some of the dressing while remaining crisp.

Toss the salad once more and taste it: If it seems too sharp, add a small pinch of sugar. If it needs more acidity, add a teaspoon of rice vinegar. Serve chilled or at cool room temperature.