Preheat the oven to 350° F. Grease a 9-by-5-inch loaf pan with cooking spray, set aside.
In a medium-sized bowl, whisk together the flour, cocoa powder, baking soda, and salt.
In a large bowl, whisk together the eggs, avocado oil, yogurt, brown sugar, and vanilla extract until combined. Pour the dry ingredients into the wet ingredients. Stir everything until combined, do not overmix.
Stir in the shredded zucchini until combined. Finally, stir in the semi-sweet chocolate chunks.
Pour the batter into the prepared pan and smooth it into an even layer. Bake for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bread to cool for about 15 minutes. Run a paring knife along the edges of the bread and carefully remove the loaf from the pan. Transfer the bread to a cooling rack. Allow it to cool before slicing.
Store in an airtight container for up to 4 days, or up to one week in the refrigerator. To freeze, wrap the loaf in plastic wrap and then foil. Freeze for up to 2 months.