Heat sugar, salt, turmeric, and vinegar in a small saucepan until the sugar melts. It does not need to boil. Let cool. Slice small zucchini and onion into a glass or metal bowl. (Plastic will stain with turmeric.) Pour vinegar solution over vegetables. Cover and put in the refrigerator for 24 hours before eating. Can keep in the refrigerator for up to a month if they last that long.