This is a recipe from King Arthur Flour. It's become my newest favorite. Dense, moist and wonderfully chocolatey, this bread is best served with a nice glass of milk.
I've tweaked the recipe a bit... you may want to visit King Arthur to see the original.
The recipe is easily doubled.

Double Chocolate Zucchini Bread

2 large eggs white sugar (1/3 cup) 3 1/2 ounces vegetable oil  (1/2 cup) 3 3/4 ounces brown sugar  (1/2 cup) 1 teaspoon vanilla extract 1 teaspoon salt 1/2 teaspoon baking soda 1/2 teaspoon baking powder 1 ounce King Arthur All-Purpose Baking Cocoa or Dutch-process cocoa (1/3 cup) 7 1/8 ounces unbleached flour (1-2/3 cups) 12 ounces shredded, unpeeled zucchini (2 cups) 6 ounces chocolate chips  (1 cup) Broken pecan pieces (1 cup) Directions 1) Preheat the oven to 350°F; lightly grease an 8 1/2" x 4 1/2" loaf pan. 2) In a large mixing bowl, beat the eggs, oil, sugars, and vanilla until smooth. 3) Add the salt, baking soda, baking powder, cocoa, and flour, mixing until well combined. 4) Stir in the zucchini, pecans and chocolate chips. *This batter will be quite thick.* 5) Pour the batter into the prepared pan. 6) Bake the bread for 65 to 75 minutes, until the loaf tests done (a toothpick or cake tester inserted into the center will come out clean, save for perhaps a light smear of chocolate from the melted chips). 7) Remove the bread from the oven, and let it cool for 10 to 15 minutes before turning it out of the pan onto a rack. 8) Cool completely before slicing; store well-wrapped, at room temperature. Yield: one 8 1/2" x 4 1/2" loaf.

Recipe summary Hands-on time: 15 mins. to 25 mins. Baking time: 1 hrs 5 mins. to 1 hrs 15 mins. Total time: 1 hrs 20 mins. to 1 hrs 40 mins. Yield: one 8 1/2" x 4 1/2" loaf