Prepare the oven by preheating to 350F (180C) from up and down, and placing an oven rack in the middle of the oven. Prepare your 9x5 inch loaf pan by lightly greasing with butter and lining with parchment paper, or by spraying with non-stick spray. Set aside.
Place shredded zucchini on a paper towel lined plate, and cover with paper towels too, pressing down to soak up the moisture. Set aside.
In a large bowl, whisk the two flours, cocoa powder, baking soda, baking powder, salt, coffee, and chocolate together until well mixed.
In another bowl, whisk together the eggs, vanilla, oil, yogurt, and sugar until completely combined. Pour the wet ingredients into the dry ingredients and lightly whisk until combined. Using a spatula, fold in the zucchini. Pour the batter into the prepared loaf pan. Sprinkle with extra chocolate if desired.
Bake for around 50 minutes or until toothpick inserted in the center comes out clean. Start checking at 45 minutes. Remove from the oven once done and let cool completely before taking the bread out of the loaf pan and slicing. Enjoy!