Peel and slice cucumber and onions thinly. The best results are even slices. I use a mandolin for this step.
Place sliced cucumber and onions in a medium bowl that has a lid.
In a small bowl mix together the Miracle Whip, sugar, vinegar. Add salt and pepper if using. Pour over top of the cucumbers/onions. Place the lid on the bowl and give it a shake or two.
Marinate 6 hours or overnight in the refrigerator.
Do not add more liquid. Juice will keep for a long time. Just keep adding onions and cucumber as they get low until you no longer get the wonderful flavor on the cucumbers. Then it is time for a new batch.