Preheat your oven to 350°F (175°C) and prepare a 9x9 inch baking pan by greasing it or lining it with parchment paper.

In a large mixing bowl, combine rolled oats, flour, brown sugar, baking soda, cinnamon, and salt.

In a separate bowl, mash the ripe bananas and mix in the egg, melted butter, and vanilla extract until smooth.

Pour the wet mixture into the dry ingredients and gently fold until just combined.

Spread the batter into the prepared baking pan evenly.

Bake for 20-25 minutes until golden brown and a toothpick comes out clean.

Let the bars cool in the pan for 15-20 minutes, then slice into squares or rectangles.