Place zucchini in the bowl of a food processor fitted with the chopping blade, and pulse until it's chopped into very small pieces. Place chopped zucchini into a large colander.
Repeat with onions, and then peppers. Place all vegetables into the colander, and toss with about 1 tablespoon salt. Stir well to combine vegetables and salt, and let sit in the colander for at least 30 minutes to release some of their liquid.
Meanwhile, mix together remaining ingredients in a large stockpot, and bring to a boil.
Add vegetables and return to a boil. Reduce heat and simmer for 30 minutes.
Remove pot from heat, and let cool to room temperature.
When liquid is cool, ladle relish with some of the liquid into sterilized jars, and seal tightly.
Discard any extra liquid, or use for another pickling project.
Refrigerate relish for at least 24 hours, and for up to 4 weeks.