Cut zucchini in half lengthwise; scoop out pulp, leaving 1/4-inch-thick shells. Sprinkle shells with salt; set shells aside. Coarsely chop pulp.
Preheat oven to 375°.
Coat a medium nonstick skillet with cooking spray, and add oil; place over medium-high heat until hot. Add chopped zucchini and onion; cook 10 minutes or until vegetables are tender, stirring occasionally. Add garlic and tomato; cook 2 minutes or until mixture is thickened, stirring occasionally. Remove from heat; stir in breadcrumbs and remaining 4 ingredients.
Spoon vegetable mixture evenly into zucchini shells. Place in a 13 x 9-inch baking dish coated with cooking spray. Cover and bake at 375° for 20 minutes. Uncover and bake 20 additional minutes or until zucchini shells are fork-tender and stuffing is lightly browned.