In a large bowl, combine zucchini, onions and pepper; sprinkle with canning salt and cover with cold water. Let stand 2 hours; rinse and drain.
In a large saucepan, bring remaining ingredients to a boil. Pour over zucchini mixture; cover and let stand 2 hours.
Transfer to a stockpot. Bring to a boil. Reduce heat; simmer, uncovered, 5 minutes. Carefully ladle hot mixture into five hot 1-pint jars, leaving 1/2-in. headspace. Remove air bubbles and adjust headspace, if necessary, by adding hot mixture. Wipe rims. Center lids on jars; screw on bands until fingertip tight.
Place jars into canner with simmering water, ensuring that they are completely covered with water. Bring to a boil; process for 10 minutes. Remove jars and cool.