Wash cucumbers under cool running water, slice thinly, sprinkle salt, and let sit in a colander for 10 minutes to extract moisture.

In a mixing bowl, combine rice vinegar, soy sauce, chili flakes, and sugar. Whisk until sugar dissolves.

Drain cucumbers, rinse under cold water, combine with dressing in a large bowl, add green onions and sesame seeds, and toss.

Chill in the refrigerator for 10-15 minutes to enhance flavor before serving.