Preheat the oven to 350° F/175°C. Line an 8''x8'' (20x20 cm) baking pan with parchment paper, Set aside.

In a large bowl combine the oil and brown sugar. Mix until combined. Add vanilla and egg, mix until fully incorporated. Add flour and stir until combined. Next, add the mashed banana and chocolate chips. Stir just until combined making sure not to over mixing. Pour into prepared pan. Bake for 20-25 minutes.

Cool for at least 10 minutes before cutting. I made really small 25 squares but you can easly cut larger ones (16 or even 9 pieces).

You can store covered in the fridge for up to a week.