Preheat oven to 350 degrees (F). Line a 9x13 inch pan with parchment paper, allowing two of the sides to overlap; spray parchment paper lightly with non-stick spray and set aside.

In a large bowl add the light brown sugar, granulated sugar, ripe mashed bananas, vanilla, oil, and eggs; beat well with a whisk to combine. Stir in the flour, baking powder, baking soda, cinnamon, nutmeg, and salt; stir until just combined. Pour batter into prepared pan, spreading smooth and into an even layer using a rubber spatula. Bake bars for 20-22 minutes, or until toothpick inserted in center comes out clean or with just a few moist crumbs attached. Place the baking pan on a cooling wrack and cool the bars completely in the pan. Once bars are completely cooled, use the overlapping sides of the parchment paper as handles to carefully life them out of the pan. Gently spread on the cream cheese frosting, and cut into squares. Serve at once, or store in the fridge, uncut, for up to 2 days.

While the cake is cooling, make your frosting!

In the bowl of a stand-mixer fitted with the paddle attachment, or in a large bowl using an electric handheld mixer, beat the cream cheese, butter, and vanilla on medium-high speed until completely smooth; about 2 minutes. Reduce the speed to low and gradually add the sifted confectioners' sugar. Once all of the sugar has been added beat on high-speed for 1-2 minutes. Once the banana bars have completely cooled, gently spread the frosting over the bars, and decorate with banana slices, if desired. Then slice and serve! Store these bars in the fridge, covered, for up to 2 days. Not that I think they'll last that long ;)