In a large bowl, combine zucchini, onions, peppers and pickling salt. Cover, and let stand at room temperature for 4 hours. Drain well; set aside.

In a large stainless steel or enamel saucepan, combine 1 cup (250 mL) vinegar, flour, dry mustard, celery and mustard seeds, allspice, turmeric, ginger, cloves and cayenne; stir until mixture is smooth. Stir in sugar, water and remaining vinegar. Cook over medium-high heat for 10 minutes, stirring often, until thickened and smooth.

Add zucchini mixture; bring to a boil over high heat. Reduce heat to medium and simmer, stirring often, for about 10 minutes, until thickened.

Immediately ladle into hot, sterilized jars, leaving 1/2 inch (1 cm) headspace. Process in hot water bath (see "Canning 101" below).

Makes 6 pint (500 mL) jars.

Canning 101
Place lids of jars in boiling water for 5 minutes. Wipe edges of jars with a clean cloth, and apply lids and screw bands until just fingertip tight. Place jars in canner filled with boiling water (water should cover jars by about 1-inch/2.5 cm).

When water has returned to the boil, start the timing and process for 15 minutes. Remove jars from canner and place on a wooden board covered with paper towels (placing hot jars on a cold, hard surface could cause breakage).

Let cool 12 to 24 hours. Check the seal (lids should curve down). Label jars, remove screw bands so they don't rust and store in a cool, dark place.