Cut the ends off the cucumber and peel lengthwise alternating to create a cucumber with stripes. Slice the cucumber into thin rounds.
Peel and slice the onion thinly and separate each slice into circles. Alternate the cucumber and onions into a 2-quart container with a lid.
Add the rest of the ingredients & cover tightly (a 2-quart jar or pitcher works well so you can gently turn the ingredients to completely mix them).
Refrigerate overnight and serve cold.