Place the zucchini, red bell pepper, yellow bell pepper, squash, red onion, mushrooms, and tomatoes in a large bowl.
In a small bowl, mix together olive oil, soy sauce, lemon juice, and garlic. Pour over the vegetables. Cover bowl, and marinate in the refrigerator for 30 minutes.
Preheat grill for medium heat.
Lightly oil grate. Remove vegetables from marinade, and place on preheated grill. Cook for 12 to 15 minutes, or until tender.
