These pickles make a great accompaniment to the famous Zuni Hamburgers served at the Zuni Caf; in San Francisco. The restaurant's chef and owner, Judy Rodgers, shared the recipe with us.
Combine zucchini and onion in a large shallow bowl. Add salt; toss to combine. Add a few ice cubes and enough cold water to cover, stirring until salt dissolves. Let stand, at room temperature, until zucchini are slightly salty and softened, about 1 hour.
Drain, removing any remaining ice cubes. Dry thoroughly between two towels, or spin, a few handfuls at a time, in a salad spinner (excess water will thin the flavor and spoil the pickle). Rinse and dry the bowl. Return the zucchini and onion to the dry bowl.
In a saucepan, combine vinegar, sugar, dry mustard, mustard seeds, and turmeric, over medium heat; simmer for 3 minutes. Remove from heat, and let stand until just warm to the touch.
Pour the cooled brine over the zucchin-and-onion mixture, stirring to combine. Transfer to sterilized jars. Cover, and refrigerate for 1 to 2 days before serving. Will keep for about 3 months, refrigerated, in an airtight container.