Vegetable Gratin
- Olive oil spray
- 2 zucchini
- 3 yellow squash
- 1 medium red or yellow onion
- 9 large plum tomatoes
- Salt and pepper to taste
- 1/4 teaspoon garlic powder (optional)
- 1/4 cup grated Parmesan cheese (optional)
- 2 to 3 tablespoons oil and vinegar salad dressing