Double Chocolate Banana-Zucchini Muffins

Preheat oven to 350°F and line a 12-cup standard muffin pan with baking cups; coat baking cups with cooking spray. Whisk together flour, cocoa, baking powder, baking soda, cinnamon, and salt in a large bowl. Make a well in the center of the mixture. Combine buttermilk, egg, honey, oil, vanilla, banana, and zucchini in a medium bowl; add to flour mixture and stir just until combined.

Fill each baking cup 2/3 full of batter, then sprinkle chocolate chips evenly over muffins. Bake for 15 minutes, until a toothpick inserted in the center comes out clean. Let muffins cool in pan on a wire rack for 2 minutes before removing from pan to serve warm or cool completely. Store leftover muffins in an airtight container at room temperature up to 2 days.