Preheat your oven to 350 degrees. Prepare your mini muffin pans with cooking spray and set aside.
Put the chocolate and 1/4 cup of oil in a glass bowl and melt in the microwave for 2 to 3 minutes at low heat, or place in the top of a double boiler over low heat, being careful not to burn the chocolate. Set aside.
In a medium bowl combine flours, cocoa, baking powder, baking soda and salt. Set aside.
In the large bowl of a stand or handheld mixer blend 1/4 cup oil and the sugar together till smooth.
Add the eggs and vanilla. Beat until blended.
Gradually add the flour mixture, then buttermilk and then the chocolate mixture.
Add the zucchini and chocolate chips, if using, and reduce speed to low until just combined.
Fill each of the mini-muffin cups to 3/4 full and bake until a toothpick inserted in the center comes out clean, between 10 to 12 minutes, or 18 to 20 minutes for standard muffin pans.
Cool in the pans for at least 5 minutes and then dump on to a rack to cool completely.
In a medium sized bowl, using a stand or hand held mixer, blend cream cheese and butter together until smooth.
Gradually add icing or powdered sugar and beat until incorporated.
Once muffins are cool spread some icing on top of each muffin. Add some chopped or shaved chocolate on top of the icing if desired! Serve and enjoy!