Using a box grater, or the shredding attachment of a food processer, shred the zucchini and onions. Set onions aside in the refrigerator.
Place shredded zucchini in a colander over a large bowl, toss with 2 tsp tablespoons salt and allow to drain in the refrigerator for at least eight hours (or upward of 24 hours).
After the draining period, discard the drained juices and gently rinse the shredded zucchini. After rinsing, squeeze out any excess moisture.
Place all ingredients in a large stock pot over medium high heat, stirring frequently. Bring mixture to a boil and continue a low boil for about 15-20 minutes or until the mixture is thickened to a relish consistency.
Ladle into sterilized pint jars, wiping the rim clean and leaving ½ inch head space. Place prepared lids and sterilized rings on jars (finger tight).
Process in a hot water bath canner for 15 minutes once the water has reached a full boil.
After processing, carefully remove from canner and allow to cool to room temperature before disturbing. Loosen or remove rings before storing.