Cut the cucumber into thin slices. Put in a bowl and season well with salt. Let them steep for 20-30 minutes so that they lose a lot of water and become soft. Then rinse the cucumbers well and squeeze out the excess moisture.
Now put the cucumbers in a bowl. Add rice vinegar, soy sauce, sesame oil, sugar, 2/3 of the spring onions and, if you like, the chili powder and mix everything well.
Pour into small bowls and decorate with toasted sesame seeds and the rest of the spring onions.