Preheat oven to 350 degrees F (175 degrees C). Grease a 9-inch baking pan with cooking spray.
Mash bananas into a paste in a large bowl. Add pumpkin pie mix, flour, brown sugar, butter, eggs, baking soda, and salt; beat with an electric mixer until creamy. Pour into the prepared baking pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 1 hour and 10 minutes.