Zucchini Chocolate Chip Coffee Cake

Preheat oven to 350 degrees. Grease well and dust with flour a bundt pan. In a bowl, sift together 2 1/4 cups flour, baking soda, baking powder, salt and cinnamon. In another bowl with an electric mixer, beat together butter and brown sugar at high speed until pale and fluffy, about 3 minutes. Beat in vanilla. Reduce speed to medium and add eggs one at a time, beating well and scraping down sides of bowl. Beat until fluffy. Reduce speed to low and add flour mixture, mixing until just combined. Toss zucchini, chocolate chips and walnuts with remaining 1/2 cup flour and then add to batter. Mix on low speed until all ingredients are combined. Spoon batter into greased bundt pan, smoothing top. Bake in middle of oven, rotating pan halfway through baking, until tester comes out clean, about 50 to 60 minutes. Cool cake in pan on a rack for 45 minutes. Invert rack over pan and invert cake onto rack. Cool completely.