Preheat oven to 350 degrees F. Grease a 9x9-inch baking pan
Combine the flour, cocoa, baking soda, and salt in a bowl and set aside.
In a medium mixing bowl add the sugar and butter. With an electric mixer beat until fluffy.
Beat the eggs in with the electric mixer.
Add the sour cream and vanilla and mix until combined.
Add the dry ingredients to the cake batter and mix until well combined.
Fold in the zucchini until it is well blended.
Spread in the prepared baking pan.
Place in the preheated oven and bake for 25 to 30 minutes. Using a wooden pick insert in the middle of the cake if the pick comes out clean or with a few moist crumbs the cake is done.
Remove from the oven and cool completely on a cooling rack.