1. In a medium bowl, whisk together oil, salt, garlic, oregano, rosemary, thyme, parsley, pepper and lemon zest and juice. Put zucchini, squash, bell peppers and onion in a large ziplock bag and pour in half of marinade. Seal bag tightly and shake well to coat vegetables. Let stand for 3 hours at room temperature to marinate. Put eggplant and mushrooms in a separate large ziplock bag, pour in remaining marinade, seal bag tightly and shake well to coat vegetables. Let stand for 1 hour at room temperature.
2. Preheat grill to medium. When heated, lightly oil grates. Grill onion, bell peppers and eggplant for 10 minutes, turning once. Add zucchini, squash and mushrooms; cook all vegetables 15 minutes longer, turning halfway through.
3. Cut vegetables into smaller sizes, if desired. Arrange on a platter and serve.