Mix zucchini, egg, buttermilk, oil and vanilla in a large mixing bowl.
Combine sugar, flour, cocoa, baking soda, baking powder and salt in a medium mixing bowl.
Add to the zucchini mixture and stir just until moistened.
Gently stir in chocolate chips.
Line 12 muffin cups with paper liners.
Fill each cup 2/3 full with batter.
Bake 350 for 25 minutes or until a toothpick inserted in the middle comes out clean.
Remove cupcakes from muffin tin and cool completely before frosting.
FROSTING
Combine cream cheese and butter and beat at a medium speed until fluffy.
Add cocoa powder, powdered sugar and milk.
Beat again until nice and fluffy.
Frost cupcakes as desired.