Preheat the oven to 350°F (180°C). Line a 9-inch square pan with parchment paper, making sure some pieces of parchment paper hang over the side to easily remove the bar from the pan later. Slightly oil the pan with cooking spray. Set aside.

Open the can of black beans, drain them over a sieve, and give them a quick rinse. Set aside in the sieve.

Mash the ripe bananas and pack the mash in measuring cups to get exactly 1 ½ cups.

Place the mashed bananas in a very large mixing bowl, add drained, black beans and use an immersion blender to blend the beans into the mashed banana. It will form a smooth puree. You can also blend everything in a food processor.

When everything is smooth, add peanut butter, vanilla extract, oats, cocoa powder, almond milk, chia seeds, chocolate chips, and walnuts.

Stir the ingredients very well, pressing them together to form a sticky, thick chocolate batter.

Pour on the prepared baking pan, press evenly, and sprinkle extra chocolate chips on top for extra sweetness, if desired. You can also do that after baking.

Bake the oat bars for 30-40 minutes at 350°F (180°C) until dry and set on top.

Let the pan cool down for 15 minutes, sprinkle extra chocolate chips now so they melt and add a delicious chocolate flavor on top. Then lift the overhanging pieces of parchment paper to release the oats onto a cooling rack.

Let it cool down completely for 1 hour before slicing into 12 bars.

Slice and serve on a plate for breakfast with a dollop of your favorite yogurt, or eat plain.