This is a no-cook recipe where most of the work involves chopping the cukes, onions, celery, and peppers. If you want more color, use more red peppers than green. I've known cooks who've added green food coloring to make it look more like the store-bought relish, but I've never felt the need for it.
Use the thick, 8-9 inch cucumbers like the one in the following photo instead of the long slender English cukes or the small pickling ones. (Update - more images below)
12 medium onions
1 celery stalk
4 green and red peppers
4 cups vinegar
6 cups white sugar
2 tsp celery seed
2 tsp mustard powder
2 tsp turmeric
1/4 cup salt
Chop the cucumbers, onions, celery stalk, and peppers into small pieces like you see in the store-bought relish.
Mix all the ingredients together making sure the sugar dissolves. The relish consistency depends on how fine you've chopped the produce. I've strained the mixture right after mixing which has thickened the relish, but wasn't as flavorful as when I've stored it with all liquid-drenched spices. If you don't strain when processing and find there's too much liquid, you can always drain some off when you open it for use.
Ladle into sterilized pint preserving jars and seal.
Yield: 9-13 pints depending if you strain first, and the size of your veggies.
UPDATE! After a bit of searching, I found these photos on the net: