Preheat oven to 350°F and line a 9"x13" baking pan with parchment paper.
In a bowl, mix together sugar, brown sugar, and eggs. Then add the oil, vanilla, sour cream, and mashed bananas. Add in the sifted flour, baking soda, baking powder, cinnamon, and salt and mix until well combined.
Pour the banana cake batter to the baking pan and bake at 350°F for 30-35 minutes or until golden and when toothpick is inserted to center comes out clean.
Once cooked, remove from baking pan and add to a cooling rack and cool compleetly.
In a large bowl, with a mixer, beat the cream cheese and butter until creamy. Add the vanilla, powdered sugar and mix beat until well combined.
Once the cake is completely cooled, spread the cream cheese frosting on top of the cake and top with chopped walnuts.