Preheat convection oven to 350°F (175°C) and grease a 9x13 inch baking pan with non-stick spray.

Sift together whole wheat flour, cocoa powder, baking soda, baking powder, and salt into a medium mixing bowl to remove lumps.

In a stand mixer fitted with a paddle attachment, cream butter with granulated and brown sugars on medium-high speed until the mixture is aerated and light.

Incorporate eggs one at a time, beating thoroughly after each addition, then mix in the vanilla extract.

Reduce mixer speed to low and add the dry ingredient mixture alternately with the sour cream, beginning and ending with the dry ingredients.

Gently fold in the grated zucchini and chocolate chips using a rubber spatula until evenly distributed throughout the batter.

Spread the batter evenly into the prepared baking pan.

Bake for 40 to 45 minutes, or until the internal temperature reaches 200°F (93°C) and a toothpick inserted into the center emerges clean.

Cool the cake completely in the pan on a wire rack to allow the crumb to set before portioning.