In a large bowl, combine flour, cocoa powder, baking powder, baking soda, salt and cinnamon.
In another large bowl, cream together butter and sugar. Beat in eggs one at a time. Add in 2 tsp orange zest, vanilla and zucchini. Stir until combined. Stir in dry ingredients.
Pour into greased bundt pan and bake for 50 to 60 minutes, or until a toothpick inserted comes out clean.
Whisk together icing sugar, orange juice and remaining orange zest. Pour over warm cake.
Recipe by Life at Cloverhill at https://lifeatcloverhill.com/2016/08/chocolate-zucchini-cake.html