Prepare the Ingredients:
Preheat the oven to 350°F (175°C).
Grease a 9x13-inch metal pan and set aside.
Mix the Batter:
In a large bowl, whisk together melted butter, oil, brown sugar, sour cream, eggs, and vanilla extract until smooth.
In a separate bowl, combine flour, cocoa powder, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing gently.
Fold in the Zucchini:
Gently fold in the shredded zucchini and chocolate chips until just combined. Do not overmix.
Bake and Cool:
Pour the batter into the prepared pan.
Bake for 40 minutes or until a toothpick inserted in the center comes out clean.
Let the cake cool completely before frosting or serving.