Place a paper towel into the bottom of a bowl. Now Slice the cucumbers into thin coins, about ¼ inch thick. 

Place the cucumbers, along with the sliced onions and green onions, into the bowl on top of the paper towel. Allow the liquid from the cucumbers to soak into the towel while you prepare the kimchi sauce.

In a small bowl combine the Korean pepper flakes, rice vinegar, soy sauce, gojuchang, sesame oil, sugar, and garlic. Stir it well until everything is fully incorporated.

Remove the paper towel from bowl with the cucumbers, and pour the kimchi sauce mixture over the cucumber and onions and stir it until everything is fully coated with the sauce.

Enjoy right away, or cover the container with an airtight lid and allow them to ferment at room temperature overnight. 

Then store them in the fridge. Sprinkle sesame seeds on them to serve (if desired).