Slice the zucchini into spears about ½ inch wide. Slice the onion, and place both in a glass or ceramic bowl. Sprinkle with the salt and add enough water to cover. Add a handful of ice cubes and let sit for 1 hour.
Meanwhile, make the brining liquid. Bring the vinegar, sugar, mustard powder and turmeric to a simmer in a small saucepan. Cook for 2-3 minutes until the sugar is dissolved. Let cool while the zucchini and onions finish soaking.
Drain the zucchini and onions and place in 2 glass jars with the dill and sliced garlic. Pour the liquid into each jar. If it does not cover the vegetables, top off with a little water.
Place the jars in the refrigerator and let it sit for a day for maximum flavor. Zucchini pickles will keep for 1 week refrigerated.