I found a recipe on RealSimple for a Marbled Chocolate zucchini bread. Here's my own modified version. Mine did not really marble much for some reason. I also used brown sugar instead of white sugar.
Marbled Chocolate Zucchini Bread
1/2 cup canola oil + 2 TBS oil(to mix with melted chocolate chips)
1 1/2 cups unbleached all purpose flour
5 ounces mini semisweet chocolate chips melted
1 1/2 tsp cinnamon
1 tsp salt
1/2 tsp baking soda
1/4 tsp baking powder
2/3 cup brown sugar (packed tightly)
2 large eggs lightly beaten
1 1/2 tsp pure vanilla extract
2 packed cups shredded zucchini
1. Heat oven to 350 degrees F.
2. Oil a 8 1/2 by 4 1/2 inch pan and dust with flour, tapping away the excess flour from pan.
3. Mix together the mini chocolate chips and the canola oil) and melt the chocolate chips in a microwave safe dish until melted and let cool until at room temp.
4. Whisk together the flour, baking powder, baking soda, cinnamon, and salt. Set aside dry ingredients.
5. In another bowl combine the wet ingredients: 1/2 cup canola oil, brown sugar, eggs, and vanilla.
6. Stir in the Zucchini to the wet ingredients.
7. Add the dry ingredients to the wet ingredients. Whisk until combined (about 1 min)
8. Pour half the batter to the loaf pan, then add half of the melted chocolate.
9. Add the rest of the batter and the remaining melted chocolate.
10. Use a butter knife to create a marble or swirl pattern.
11. Bake until a toothpick inserted into the center comes out clean (60-70minutes)