Pre-heat the oven to 350 °F.
Line a 9-inch square pan with parchment paper; slightly oil the paper with cooking spray; set aside.
Mash the ripe banana, pack in measuring cups to get exactly 2 cups.
Place the mashed bananas in a mixing bowl, add peanut butter, oats and chocolate chips; stir very well until it's consistently combined and thick.
Pour into the prepared baking pan, press evenly and sprinkle extra chocolate chips on top, if desired.
Place in the pre-heated oven and bake for 30 - 40 minutes until dry and golden on top.
Remove from the oven and allow the pan cool down for 15 minutes,
Lift the overhanging pieces of parchment paper to release the oats onto a cooling rack.
Let it cool completely for 2 - 3 hours before slicing.
Slice and serve on a plate for breakfast with fruits, yogurt or plain.