Preheat your oven to 350°F (175°C). Grease and flour a 9×13-inch baking dish or line it with parchment paper.

1. In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, salt, and cinnamon (if using). Set aside.
2. In a large bowl, beat together the eggs, sugar, oil, and vanilla extract until smooth and well combined.
3. Add the grated zucchini to the wet ingredients and mix well. There’s no need to squeeze out the moisture from the zucchini; it will keep the cake moist.
4. Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Be careful not to overmix.
5. If using, fold in the chocolate chips and nuts.
6. Pour the batter into the prepared baking dish and spread it out evenly.
7. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs.
8. Allow the cake to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely before slicing.
9. Optionally, dust with powdered sugar or top with frosting if desired.