Heat oven to 350°F. Heat oil in medium skillet over medium heat until hot. Add onion; cook and stir 3 minutes or until tender. Add roasted peppers, broccoli in sauce, and mushrooms; cook 2 to 3 minutes or until broccoli is crisp-tender, stirring occasionally.
Cut each zucchini in half lengthwise. Scoop out center, leaving 1/4-inch shell. Spoon broccoli mixture into each zucchini half. Place in ungreased 12x8-inch (2-quart) glass baking dish.
In small bowl, combine bread crumbs and butter; mix well. Sprinkle over stuffed zucchini. Cover with foil.
Bake at 350°F. for 20 minutes. Uncover; bake an additional 8 to 12 minutes or until topping is golden brown and vegetables are tender.