Place zucchini in a colander; sprinkle with salt. Toss well. Drain 30 minutes, tossing occasionally. Place zucchini on paper towels; squeeze until barely moist.
Carefully remove rind from lemon using a vegetable peeler, making sure to avoid white pithy part of the rind. Place rind in a small saucepan; cover with water. Bring to a boil; cover, reduce heat, and simmer 15 minutes or until rind is tender. Drain; cool. Finely chop rind.
Combine zucchini, rind, onion, and the remaining ingredients in a large saucepan; bring to a boil. Reduce heat, and simmer, uncovered, 35 minutes or until thick, stirring frequently. Cool; pour into airtight containers.
Note: Refrigerate Lemon-Zucchini Relish in airtight containers up to a month.