Preheat the oven to 375 degrees F and spray a muffin tin with cooking spray. I lined my pan with cut parchment to make them look a bit more like they are from the bakery.

Make the crumb topping. Place butter, sugar, flour, and cocoa powder into a medium-sized bowl and press with a fork until you have a coarse bread crumb texture. Set aside.

In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda and salt until well combined.

In another bowl, whisk together the oil, milk, eggs, vanilla, sugar, and brown sugar until smooth and well combined.

Stir in the grated zucchini.

Add the wet mixture to the dry ingredients and stir until just combined.

Fold in the chocolate chips.

Fill the prepared muffin tin until the cups are 3/4 full. Sprinkle a tablespoon of the crumble topping on each muffin and bake for 20-22 minutes, or until an inserted toothpick comes out clean.

Cool for 5 minutes in the muffin tin, then remove the muffins to a wire rack to cool completely.