Spray an 8x8 square pan with non-stick spray or line it with parchment. (I adore using the dual foil-parchment paper as it molds nicely to pans but still provides the non-stick awesomeness of parchment paper!)
In a microwaveable bowl, combine butter with brown sugar. Microwave on high for 2 minutes 30 seconds.
Add oatmeal, stir and return to the microwave for an additional 2 minutes.
Stir in vanilla. Measure out about 3/4 cup of the oat mixture and press remaining mixture into the 8x8 pan. Slice banana and spread around on top of the oat mixture.
Combine chocolate chips and peanut butter and microwave on high for 2 minutes. Stir until combined and spread over bananas. Sprinkle remaining 3/4 cup oats onto the chocolate. Refrigerate 2-3 hours. Cut into squares and enjoy!
Store any remaining bars in the fridge.