Wash cucumbers thoroughly and slice them into thin rounds, about ¼ inch thick. Sprinkle with salt and let sit in a colander for about 10 minutes.

In a medium-sized mixing bowl, combine rice vinegar, soy sauce, chili flakes, sugar, and sesame oil. Whisk until sugar dissolves.

Rinse cucumbers under cold running water to remove excess salt. Pat dry. In the mixing bowl with the dressing, add cucumbers, sesame seeds, and green onions. Toss gently.

Transfer salad to a serving bowl and let it sit for at least 15 minutes before serving.