Preheat your oven to 350°F (175°C) and line a muffin tin with muffin liners or grease it lightly.
Grate the zucchini using a grater and set it aside to drain slightly.
In a mixing bowl, combine the whole wheat flour, cocoa powder, rolled oats, baking powder, baking soda, salt, and ground cinnamon. Whisk the dry ingredients together until well mixed.
In another bowl, whisk together the maple syrup (or honey), applesauce, vegetable oil, eggs, and vanilla extract until combined.
Add the grated zucchini to the wet ingredients and mix well.
Pour the wet ingredients into the bowl of dry ingredients. Using a rubber spatula, gently fold everything together until just combined. Be careful not to overmix.
If desired, fold in the chocolate chips.
Portion the batter into the prepared muffin tin, filling each muffin cup about ¾ full.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Once baked, remove them from the oven and let them cool in the tin for a few minutes before transferring them to a wire rack to cool completely.