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

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

In a separate bowl, mash the very ripe bananas until smooth. Add the egg, melted butter, and vanilla extract, and blend thoroughly.

Fold the wet banana mixture into the dry ingredients, stirring until just combined. Avoid overmixing.

Pour the batter into the prepared pan and spread it evenly. Smooth the top with a spatula.

Bake in the preheated oven for 20-25 minutes. They are done when the edges are golden brown and a toothpick comes out clean.

Let the bars cool completely in the pan before cutting into 12 bars.