Preheat the oven to 375°F and line a 12-cup muffin pan with paper liners.
Whisk the all-purpose flour, baking powder, baking soda, salt, and cinnamon together until evenly combined.
In a separate bowl, whisk the mashed banana, brown sugar, Greek yogurt, oil, milk, and vanilla until smooth and creamy.
Add the dry ingredients to the banana mixture and fold just until no dry streaks remain. Fold in the mini chocolate chips without overmixing the batter.
Divide the batter evenly among the 12 muffin cups, filling each about three-quarters full.
Bake for 18 to 22 minutes, until the tops spring back when lightly pressed and a tester inserted into the center comes out without wet batter. Cool in the pan for 10 minutes before transferring the muffins to a rack.
