Preheat oven to 350 degrees F. Spray 9x13 inch pan with oil spray.
In a bowl, cream together the butter, peanut butter, salt, and sugars with an electric mixer at high speed.
Add eggs, one at a time, while mixing at medium speed. Add vanilla and bananas, continuing to beat at medium speed.
In a small bowl, add cocoa and flour and mix together. Add dry ingredient to wet ingredients and mix together by hand till well incorporated. Fold in chocolate chips.
Pour batter into pan and bake until top feels firm and a toothpick inserted comes out clean, 15 to 20 minutes.
Allow to cool before serving.