Peel and slice cucumber. Slice onion. You want everything thin enough that you don't have giant chunks, but not so thin that everything just falls apart. *Note - even if you do NOT like onion, do NOT omit. My husband loves the onion in this, I do not. But, I tried making this recipe without the onion and the flavor was all off. So, if you don't like onion, just don't eat any of them when you dish it up! ;)Dump the cucumber and onion into a large serving dish. Add vinegar and water--enough to cover the vegetables. As long as you keep the vinegar & water ratios about 1 part to 2 parts, you should be good!Season with salt & pepper to taste (I don't add much).Cover and refrigerate. If you can make it overnight, that's best. They are SO good after they've been sitting for at least 12 hours. 24 is even better!!