Prep: Preheat the oven to 350°F. Grease the bottom and sides of a 9 X 13 dish with nonstick spray and set aside.
Batter: In a large bowl, mash the bananas, and add the sugar and stir until well blended. Add the vegetable oil, eggs. and Vanilla. Stir well, until all ingredients are fully incorporated.
In a separate bowl, whisk the flour, baking powder, baking soda, cinnamon, and salt. Add the dry mixture to the bowl of wet ingredients and stir to mix.
Bake: Pour into the 9 X 13 dish, and place the dish in the oven. Bake for 25 minutes, or until a toothpick inserted in the center of the bars comes out clean. Remove from the oven to a wire rack, and cool completely before topping with frosting.
Frosting: In the mixing bowl of a stand mixer, add the cream cheese, butter, and vanilla, and mix until smooth. Add the powdered sugar a little at a time, mixing between additions, until all the powdered sugar has been added, and the frosting is thick and creamy.
Frost the banana bars, using all the frosting, and allow the frosting to set, for about 30 minutes. You can place the bars in the refrigerator to cool completely, and keep frosting cool. Slice, serve, and enjoy!