Finely chop zucchini, onions, bell pepper. (I used my food processor to do this, but feel free to do it by hand.) Combine, and add salt. Cover & let stand 2+ hours, or overnight.
Drain zucchini mixture. Rinse, and allow to drain well. Squeeze out remaining moisture (zucchini will sweat more in the pot). Transfer to large stockpot/saucepan.
In a medium saucepan over medium-high heat, combine remaining ingredients. Bring to a boil and allow mixture to thicken, about 5-8 minutes. Add vinegar solution to zucchini, stirring to incorporate. Bring to a boil, reduce to simmer 20 minutes, stirring frequently.
Prepare traditional canning bath. Process jars 10 minutes. Let jars sit 12 hours; label and store.