Preheat the oven to 350 degrees F (175 degrees C). Line a muffin tin with paper liners.
Combine flour, cocoa, baking powder, baking soda, and salt together in a large bowl.
Whisk sugar, oil, egg, milk, and vanilla extract together in a separate bowl. Stir into flour mixture until just moistened. Fold in bananas and chocolate chips.
Divide batter among the muffin cups, filling each about 3/4 full.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 20 to 25 minutes.
Substitute yogurt for the milk if preferred.
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