Preheat the oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper.

In a large mixing bowl, mash the bananas with a fork until they reach a smooth consistency with minimal lumps.

Add the peanut butter and ground cinnamon to the mashed bananas, stirring until the mixture is homogeneous.

Fold in the rolled oats and dark chocolate chips until the dry ingredients are fully incorporated and moistened.

Transfer the batter to the prepared baking pan and use a spatula to press it into an even layer.

Bake for 18 to 20 minutes, or until the edges are lightly browned and the center is firm to the touch.

Remove from the oven and allow the bars to cool completely in the pan before slicing into 9 squares.