Cut zucchini in half lengthwise; scoop out pulp, leaving 1/4-inch thick shells. Sprinkle shells with salt, set aside. Coarsely chop pulp.
Coat a medium nonstick skillet with cooking spray; add oil, place over medium-high heat until hot. Add chopped zucchini and onion, cook 10 minutes or until vegetables are tender, stirring often.
Add garlic and tomato, cook 2 minutes or until 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- x 2-inch baking dish coated with cooking spray. Cover and bake at 375 degrees F for 20 minutes. Uncover and bake 20 additional minutes or until zucchini shells are fork-tender and stuffing is lightly browned.