Combine zucchini, onion, green and red peppers; sprinkle with salt; cover with cold water. Let stand 2 hours. Drain; rinse and drain thoroughly.
Combine remaining ingredients in a large saucepan.
Bring to a boil.
Add vegetables; simmer 10 minutes.
Pack hot relish into hot jars, leaving ¼ inch headspace.
Remove air bubbles. Adjust two-piece caps.
Process 10 minutes in a boiling-water canner.