Peel and thinly slice the cucumbers. Slice the onion thinly.
Seed and thinly slice the chile. Put the cucumber slices in a shallow bowl, arrange the onion slices on top and sprinkle with the chile slices.
Combine all the ingredients with the dressing, mixing well.
Taste and adjust seasoning with salt. Pour the dressing over the onions and cucumbers and refrigerate a few hours or overnight if possible to allow flavors to blend