Gather all ingredients.

Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 9x13-inch baking pan.

Mix flour, sugar, cocoa, baking soda, baking powder, cinnamon, and salt together in a medium bowl.

Add oil and eggs; mix well until just combined.

Fold in shredded zucchini and walnuts until just combined.

Pour cake batter into the prepared pan.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 50 to 60 minutes.

Cool cake completely before frosting with your favorite frosting.