3 cups all-purpose flour
3/4 cup sugar
1 1/2 teaspoons baking powder
1 teaspoon baking soda
1/2 teaspoon salt
2 egg whites
1 egg
1 1/3 cups fat-free plain yogurt
1/3 cup canola oil
2 cups shredded zucchini, patted dry
4 teaspoons vanilla extract, divided
1 tablespoon dry bread crumbs
1/3 cup packed brown sugar
1/3 cup chopped walnuts
1/3 cup raisins
1 tablespoon ground cinnamon
1/2 teaspoon ground allspice
3/4 cup confectioners' sugar
2 teaspoons fat free milk