In the bowl of a stand mixer, beat butter and sugar until creamy.
Add in eggs, vanilla, and orange zest beating well after each addition.
Add in milk, oil, and baking cocoa.
In a separate bowl, combine flour, baking powder, baking soda, and salt.
Add flour to cocoa mixture gradually, beating well after each addition.
Gently fold in zucchini.
Spread batter into a well greased Bundt pan.
Bake at 350 degrees for 50-55 minutes, or until a cake tester comes out clean.
Cool completely on a wire rack.
For frosting, beat powdered sugar, butter, and cocoa.
Drizzle 1/2 tablespoons of orange juice and milk, alternately, until spreadable frosting consistency is achieved.
Spread over cooled cake.