Wash the cucumber thoroughly and peel partially.
Slice the cucumber diagonally into bite-sized pieces, then gently smash with a rolling pin to create a 'smashed' texture.
Mince the garlic and slice the onion thinly.
In a bowl, combine cucumber, garlic, onion, salt, vinegar, sesame oil, and chili powder. Toss lightly.
Serve in a dish and sprinkle sesame seeds on top to finish.