First cut the cucumber into very thin slices. You can use a mandolin. It would make your work easy. Otherwise you can also make thin slices using a sharp knife. You can leave the skin on for added color and texture.
In a small bowl, whisk together the rice vinegar, soy sauce, sugar, sesame oil, and grated ginger. The sauce for Sunomono salad is ready.
In a larger bowl add sliced cucumbers and cover it with salt. Leave these cucumbers at rest for at least 15 minutes.
After 15 minutes squeeze the water from the cucumbers.
Pour the dressing over the cucumbers and toss well to coat. Leave these cucumbers at rest for at least 15 minutes.
Cover the bowl and refrigerate for at least 30 minutes. This allows the flavors to meld. Before serving, sprinkle the salad with toasted sesame seeds.