Preheat oven to 325 degrees. Line cup cake liners in a medium cupcake baking tray. Mix first 6 ingredients together in a bowl. In another large bowl, mix next 6 ingredients, until creamy. Add the dry ingredients to the wet with zucchini and chocolate chips. Poor into prepared cup cake pans. Bake on the center rack, for 22-25 minutes, or until slightly browned on top. Remove from oven and cool completely before frosting. For frosting, in a medium bowl, sift the confectioners sugar, cocoa, and cinnamon together, then set aside. In a large bowl, cream butter until smooth, then gradually beat in sugar mixture and slowly blend in the milk and vanilla. Beat on high speed until light and fluffy. Pour into a large resealable bag and snip off a corner about 1/2 inch. Pipe onto cupcakes, starting in the center as if making a small letter e.