Preheat the oven to 350°F.
In a large mixing bowl, cream the butter and sugars together for 2-3 minutes using an electric hand mixer.
Add the milk, eggs, and zucchini. Mix again until the eggs are fully incorporated into the batter.
Whisk in the baking powder, baking soda, cocoa powder, and flour on medium speed until the batter is smooth and homogenous.
Fold in the chocolate chips until they are evenly distributed throughout the mixture.
Spray a muffin tin with nonstick cooking spray. Divide the batter among the tin and bake for 20 minutes.
Allow the muffins to cool in pan for 10 minutes before removing and placing on wire rack.
Prepare the frosting by whipping all of the frosting ingredients together in a large bowl. Mix until smooth and creamy.
Frost the muffins, serve, and enjoy!