Preheat your oven to 350°F (177°C) and line a 12-cup muffin tin with paper liners.
In a large mixing bowl, whisk together the flour, baking powder, baking soda, salt, and brown sugar until well combined.
In a separate bowl, beat the mashed bananas with the melted butter, egg, and vanilla extract until the mixture is smooth and cohesive.
Gradually fold the wet ingredients into the dry mixture, stirring just until no dry streaks remain. Be careful not to overmix.
Gently fold in the chocolate chips until they are evenly distributed throughout the batter.
Divide the batter evenly among the muffin cups, filling each about three-quarters full.
Bake for 20 to 25 minutes, or until a toothpick inserted into the center of a muffin comes out clean. Allow the muffins to cool in the tin for a few minutes before transferring them to a wire rack to cool completely.