In a large bowl, beat the zucchini, yogurt, sugar, egg whites, oil, egg and 3 teaspoons vanilla until well blended. In a small bowl, combine the flour, baking powder, baking soda and salt; gradually beat into zucchini mixture until blended.
Coat a 10-in. fluted tube pan with cooking spray; sprinkle with bread crumbs.
Pour a third of the batter into pan.
Combine the brown sugar, walnuts, raisins, cinnamon and allspice; sprinkle half over batter. Top with another third of the batter.
Sprinkle with remaining brown sugar mixture; top with remaining batter.
Bake at 350 for 55-65 minutes or until a toothpick inserted near the center comes out clean. Cool for 10 minutes before removing from pan to a wire rack to cool completely.
In a small bowl, combine confectioners' sugar, remaining vanilla and enough milk to achieve desired consistency; drizzle over cake.