Preheat oven to 350 degrees. Grease 2 loaf pans (8 ½ x 4 1½) with nonstick cooking spray.Microwave butter in a large bowl for one minute, or until melted. Stir sugars into butter until completely smooth. Stir in eggs and vanilla.
In a medium-sized bowl, whisk flour, cocoa powder, salt, baking powder, and baking soda. Add dry ingredients to the butter mixture. Stir until well combined. The batter will be very thick.
Stir in shredded zucchini and 1 ½ cups chocolate chips.Divide the batter equally between the two prepared loaf pans. Evenly spread the batter in the pans. Sprinkle the remaining ½ cup chocolate chips on top of the loaves before baking.
Bake for 60-70 minutes, or until a toothpick inserted into the center of the loaf comes out clean (except for maybe a little melted chocolate from the chocolate chips). Allow loaf loaves to cool in pans on a cooling rack for 10 minutes, then turn loaves out onto the rack to cool completely.
Notes
To freeze, completely cover the loaf in plastic wrap twice. Wrap again in aluminum foil or place the wrapped loaf in a resealable freezer bag. Freeze for up to 3 months. Thaw overnight in the refrigerator before serving.