Smash the cucumber: Wash and dry the cucumber. Using the side of a large knife or rolling pin, gently smash the cucumber until it splits into rough segments. Slice it at a diagonal into bite-sized pieces.
Mix it up: In a mixing bowl, toss the smashed cucumber with salt, sugar, sesame oil, soy sauce, and rice vinegar, minced garlic, chili oil (if using), and chopped cilantro until fully dissolved.
Garnish: Finish with a sprinkle of toasted sesame seeds and serve immediately, or chill for 10–15 minutes for deeper flavor.
