In a large bowl, whisk together the vegetable oil, buttermilk, and granulated sugar until well-combined.
⅓ cup vegetable oil, ⅔ cup buttermilk, 1 cup granulated sugar
Whisk in eggs and vanilla extract until incorporated.
2 large eggs, 1 teaspoon vanilla extract
Add the zucchini, and whisk until combined.
1 cup zucchini grated
Add flour, cocoa powder, baking powder, baking soda, and salt. Whisk until just combined.
1 ½ cups sifted all-purpose flour, ⅓ cup unsweetened cocoa powder, 1 teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon salt
Whisk in the chocolate chunks and chopped nuts.
¾ cup semisweet chocolate chunks, ½ cup chopped walnuts or pecans
Pour the batter into the prepared pan.
Bake 45-60 minutes, or until a toothpick inserted in the center comes out clean.
Let cool in pan for 10 minutes.
Remove from pan, and let cool completely on a wire cooling rack.
Video
Notes
Oil: Feel free to substitute a similar oil like olive oil or canola oil.
Buttermilk: Regular or low-fat buttermilk will work. If you don't have buttermilk, you can make a homemade buttermilk substitute.
Chocolate chunks: Milk chocolate chunks will give you a sweeter bread and bittersweet chocolate chunks will give you a less sweet loaf. Chocolate chips could also be used in place of the chocolate chunks.
Nuts: If you don't like nuts, you can either leave them out, or you can add in more chocolate chunks.