Preheat the oven to 350°F (175°C) and grease a donut pan.

In a mixing bowl, whisk together the dry ingredients: flour, cocoa powder, baking powder, baking soda, and salt.

In another bowl, combine the grated zucchini, sugar, brown sugar, vegetable oil, eggs, and vanilla extract until well mixed.

Gradually add the dry ingredients to the wet ingredients, stirring until just combined.

If using, fold in the chocolate chips.

Spoon the batter into the prepared donut pan, filling each cavity about 3/4 full.

Bake in the preheated oven for 15-20 minutes or until a toothpick inserted comes out clean.

Allow the donuts to cool in the pan for a few minutes before transferring to a wire rack.

Dust with powdered sugar if desired and serve warm or at room temperature.