Sauté onion and garlic in 2 tablespoons olive oil until tender. Remove from heat; stir in breadcrumbs. Set aside. Cut each zucchini into 4 lengthwise slices leaving slices attached on stem end. Fan slices out, and place in 15x10x1-inch jellyroll pans; brush zucchini fans lightly with remaining 2 tablespoons olive oil.
Sprinkle each zucchini fan lightly with 1/2 teaspoon breadcrumb mixture. Bake at 350F for 15 to 20 minutes or until crisp-tender