Bring a large pot of salted water to a boil. Add the cavatappi and cook according to the package directions. Drain and rinse under cold water. Set aside.
Meanwhile, soak the onion in cold water for 5 minutes and then drain.
Whisk together the mayonnaise, sour cream, cider vinegar, oil, sugar, mustard, drained red onion, 1/2 teaspoon salt and a few grinds of pepper until smooth.
Add the cooked cavatappi, tomatoes, dill, corn and zucchini to the dressing and stir to coat.
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