1. In a large bowl, combine the sliced zucchini, halved and sliced onion, chopped tomato, and fresh basil. 2. Pour the bottled Italian dressing over the vegetable mixture. Season with salt and pepper to taste. 3. Transfer the mixture to a storage container, cover, and refrigerate for at least 3 hours to allow the flavors to meld. 4. Before serving, sprinkle the freshly grated Parmesan cheese over the top.