Preheat your oven to 350°F (175°C) and line an 8x8 inch baking dish with parchment paper, leaving some overhang for easy removal.
In a large mixing bowl, combine the rolled oats, mashed bananas, almond butter, honey (or maple syrup), vanilla extract, cinnamon, and salt. Stir until well combined.
Gently fold in the mixed berries, being careful not to crush them if using fresh berries.
Pour the mixture into the prepared baking dish and spread it evenly with a spatula.
Bake for 25-30 minutes, or until the edges are golden brown and the center is set.
Allow the bars to cool in the pan for about 10 minutes, then lift them out using the parchment paper and let them cool completely on a wire rack before cutting into squares.