Place sliced cucumbers in a colander, sprinkle with 1 teaspoon salt, 1 teaspoon sugar, and let sit for 10–15 minutes in the refrigerator. Pat dry to remove excess water.
In a small bowl, whisk together rice vinegar, soy sauce, sesame oil, sugar, red pepper flakes, and garlic.
Toss cucumbers with the dressing until well coated.
Sprinkle with sesame seeds and optional green onions. Chill for 20–30 minutes before serving for best flavor. Toss before serving and enjoy!