1. Slice the cucumbers in 1/8 inch slices (a food processor is great for this). If you are using garden cucumbers, you will want to peel them and remove the seeds before slicing.
2. In a small bowl, stir together the onions, vinegar, sugar and a pinch of salt and pepper.
3. Place the cucumber slices in a serving bowl, and toss with the dressing. You can leave this to marinate several hours in the refrigerator.

Makes 4 servings.