Slice Cucumber: Wash the cucumber, cut off the ends, and slice it thinly using a slicer.
Add Salt: Place the slices in a medium bowl and sprinkle with salt. Let the cucumbers sit for about 5 minutes.
Soak Seaweed: While the cucumbers are sitting, take a small bowl and soak the dried wakame seaweed in cold water for about 5 minutes until it is rehydrated. Drain the seaweed completely.
Add Seasoning: Once the cucumbers have sat for 5 minutes, remove any excess water and add rice vinegar, sugar, and soy sauce to the bowl. Toss the cucumbers well with the seasoning.
Add Wakame Seaweed: Finally, add the rehydrated wakame seaweed to the bowl and toss everything together.
Topping: Sprinkle toasted white sesame seeds over the salad.
Notes
Storage: Transfer the salad to an airtight container and store it in the refrigerator. It will keep well for 3 to 4 days.
You don't need to peel Japanese cucumbers as they have thin skin. However, if you pick a different type of cucumber that has a bitter, thick skin, then you may want to peel them before use.
By salting the cucumbers to draw out excess water, they won't become watery when mixed with the seasonings.