Preheat oven to 350°F. Line the loaf pan with parchment paper and secure with metal clips (see recipe post for picture), or spray with nonstick spray. Set aside.
Prepare the Chocolate Streusel Topping: In a small bowl, mix together the granulated sugar, flour, cocoa powder, salt, and melted butter. Stir until fully combined. Then add the mini chocolate chips and toss until incorporated. Set aside.
In a large bowl, stir together the dry ingredients for the bread, including the flour, cocoa powder, baking soda, cinnamon, and salt until fully combined. Set aside.
In a separate mixing bowl, whisk together the wet ingredients for the bread, including the vegetable oil, yogurt, eggs, brown sugar, granulated sugar, and vanilla.
Add the wet mixture to the dry mixture and stir until fully combined. The batter will be thick.
Add the shredded zucchini to the bread batter and stir to combine. Fold in the mini chocolate chips. Pour the bread batter into the prepared loaf pan. Sprinkle the Chocolate Streusel Topping to cover the top of the loaf.
Bake for 50-60 minutes or until a toothpick inserted in the center comes out clean. Allow loaf to cool in the pan for 15 minutes before removing and transfer to a wire cooling rack. Allow loaf to cool completely before slicing.
To store loaf, wrap in plastic wrap and keep on counter for up to 5-6 days. You can also freeze the loaf in a zip top freezer bag for up to three months.