Slice the onion thinly and cut the cucumber lengthwise in half, then slice diagonally.

In a mixing bowl, combine red pepper powder, soy sauce, minced garlic, sugar, and sesame oil to create the dressing.

Add the prepared cucumber and onion to the bowl.

Mix gently with your hands until the vegetables are evenly coated with the dressing.

Sprinkle sesame seeds on top and give it a final mix.