Rinse the cucumbers well and slice them thinly into rounds or half-moons as you like.
Put the cucumber slices into a bowl, sprinkle with salt, and toss to mix. Let them rest for around 10 minutes to draw excess water out.
In a different bowl, whisk together the rice vinegar, soy sauce, chili flakes, sugar, sesame oil, and minced garlic if you choose to include it until the sugar dissolves.
Drain the cucumbers and rinse with cold water to remove some saltiness, then gently pat them dry with a towel.
Pour the dressing over the cucumbers and toss everything together so each slice is coated evenly.
Add the chopped green onions and sprinkle sesame seeds on top, then stir gently to blend the flavors.
For the best taste, chill the salad in the fridge for about 20 minutes before serving to let the flavors combine nicely.