Preheat the oven to 350ºF and grease a 9x13 inch pan.
In a large bowl, mix together the grated zucchini, brown sugar, applesauce, eggs, and vanilla extract until well combined.
In another bowl, stir together the flour, cocoa powder, baking soda, baking powder, cinnamon, and salt.
Gradually add the dry mixture to the wet ingredients and stir until just combined.
Gently fold in the chocolate chips or nuts into the batter.
Pour the brownie batter into your prepared pan and spread it evenly. Bake for about 55 minutes or until a toothpick inserted in the center comes out clean.
Once cooled, feel free to frost with your favorite frosting or enjoy them as-is.