Preheat oven to 400 degrees Fahrenheit. Line 12 muffin cups with cupcake liners.
In a large bowl, stir together the flour, sugar, baking powder, and salt. Make a well in the center of the flour mixture and then set aside.
In a medium bowl, combine the mashed banana, egg, milk, and oil.
Add the egg mixture all at once to the flour mixture and stir just until moistened. Batter will be lumpy.
Fold in the chocolate chips into the muffin batter.
Spoon batter into prepared muffin cups, filling each 2/3 full.
Bake for 18-20 minutes or until golden and a toothpick inserted comes out clean.
Cool in muffin cups for 5 minutes. Remove from muffin cups.