Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.

In a bowl, mash the bananas until smooth. Add the beaten egg and vanilla extract, mixing until combined.

In another bowl, combine rolled oats, cinnamon, salt, and baking powder.

Add the dry ingredients to the banana mixture, stirring until just combined. Avoid overmixing.

Scoop tablespoon-sized amounts of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Bake for 12-15 minutes or until the edges are lightly golden and the tops are set.

Remove from oven and let cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.