In a large bowl, combine the sliced zucchini and onion. Sprinkle with salt and toss to coat. Let stand for 1 hour, then drain and rinse thoroughly.
In a large non-reactive saucepan, combine the white vinegar, granulated sugar, celery seed, mustard seed, and turmeric. Bring to a boil, stirring until the sugar is dissolved.
Add the drained zucchini and onion mixture to the boiling syrup. Return to a boil, then reduce heat and simmer for 5 minutes.
Pack the hot pickles and syrup into clean jars. Let cool to room temperature, then cover and refrigerate.
Notes
Best served after chilling in the refrigerator for at least 24 hours to allow flavors to meld.