Gather all ingredients. Preheat the oven to 325 degrees F (165 degrees C). Grease and flour a 9x13-inch baking dish.

Combine milk and vinegar in a large bowl; let stand to sour milk, about 5 minutes.

Meanwhile, combine flour, cocoa powder, baking soda, and baking powder in a medium bowl.

Add sugar, butter, oil, eggs, and vanilla to soured milk; beat until incorporated. Add flour mixture; stir until just combined. Fold in zucchini.

Pour batter into the prepared baking dish. Sprinkle with chocolate chips.

Bake in the preheated oven until a toothpick inserted into the center of cake comes out clean, about 45 minutes. Transfer to a wire rack to cool completely.