Preheat oven to 375°F. Scoop out pulp from zucchini halves, then chop pulp and set aside. Arrange zucchini halves on baking sheet; set aside.
Heat olive oil in large skillet over medium heat. Cook garlic and onions, stirring occasionally for 1 minute. Add zucchini pulp and mushrooms and cook, stirring occasionally, 5 minutes or until tender. Stir in parsley and sauce.
Evenly fill zucchini halves with vegetable mixture, then top with bread crumbs. Bake 30 minutes or until zucchini are tender.