This recipe is from the Joy of Baking website. It is the best zucchini recipe I've ever tried! I used half whole wheat flour & half all-purpose flour and I've never had a problem with the bread drying out.
Preheat oven to 350 degrees F (180 degrees C) and place rack in the center of the oven. Grease (or spray with a nonstick vegetable spray) a 9 x 5 x 3 inch (23 x 13 x 8 cm) loaf pan. Set aside.
Grate the zucchini, using a medium sized grater. Set aside.
In a large bowl whisk together the flour, cocoa powder, baking soda, baking powder, salt, ground cinnamon, and ground allspice. Set aside.
In the bowl of your electric mixer (or with a hand mixer), beat the oil, sugars, eggs, and vanilla extract until well blended (about 2 minutes). Fold in the grated zucchini. Add the flour mixture, beating just until combined. Then fold in the chocolate chips. Scrape the batter into the prepared pan and bake until the bread has risen and a toothpick inserted in the center comes out clean, about 55 to 65 minutes. Place on a wire rack to cool for about 10 minutes, then remove the bread from the pan and cool completely.