Heat oven to 350°F. Line two baking sheets with parchment.
Mash bananas in a bowl until mostly smooth; set aside.
Cream butter, brown sugar, and granulated sugar until light and fluffy, 2 minutes.
Beat in the beaten egg and vanilla until combined.
Stir in the mashed bananas until evenly incorporated.
Whisk flour, baking powder, baking soda, cinnamon, and salt in a separate bowl.
Add dry ingredients to wet and mix just until no dry streaks remain.
Fold in chocolate chips, if using. Rest batter 5 minutes.
Scoop 1½-tablespoon mounds onto sheets, spacing about 2 inches apart.
Bake 10–12 minutes, until edges set and tops look puffed.
Cool 5 minutes on the pan, then move to a rack to finish cooling.