1. Trim the ends from the zucchini and cut lengthwise into 1/16-inch-thick slices. Cut the onion in half around the pole axis, peel the outer skin, and cut crosswise into thin slices. Transfer the vegetables to a large, non-reactive bowl.
2. Dissolve the kosher salt in one quart of water and pour over vegetables. Add the ice to the bowl, and fill with enough water to cover. Let rest at least one hour.
3. Combine the remaining ingredients in a small saucepan and stir until combined. Place over medium-high heat and simmer.
4. Drain and rinse the cucumbers-onion mix and pack into hot pint jars. Pour the liquid over the vegetables, screw on two-piece canning lids, and process in a hot-water bath according to the USDA-recommended times for your area.