Preheat oven to 350°.
To prepare cake, coat a 12-cup Bundt pan with cooking spray; dust pan with 1 tablespoon flour.
Place sugars, cream cheese, and vegetable oil in a large bowl, and beat with a mixer at medium speed until well blended (about 5 minutes). Add eggs and egg whites, 1 at a time, beating well after each addition. Beat in 1 teaspoon vanilla extract.
Lightly spoon 2 1/2 cups flour into dry measuring cups, and level with a knife. Combine 2 1/2 cups flour and next 5 ingredients (2 1/2 cups flour through cinnamon) in a medium bowl, stirring well with a whisk.
Add flour mixture and buttermilk alternately to sugar mixture, beginning and ending with flour mixture. Stir in zucchini, 2/3 cup chocolate chips, and nuts. Pour batter into prepared pan. Bake at 350° for 1 hour or until a wooden pick inserted in cake comes out clean. Cool in pan 10 minutes on a wire rack; remove from pan. Cool completely on wire rack.
To prepare glaze, combine 3/4 cup powdered sugar and 3 tablespoons cocoa in a small bowl; stir with a whisk. Combine milk, 2 tablespoons chocolate chips, coffee, and 1/2 teaspoon vanilla extract in a 1-cup glass measure. Microwave at medium 45 seconds or until chocolate melts, stirring after 20 seconds. Combine powdered sugar mixture with chocolate mixture, stirring with a whisk. Drizzle glaze over cake.