Preheat the oven to 350 degrees. Grease and flour a 9-inch cake pan.
Using mixer, mix the mashed bananas and sugars on low speed until combined. Add the oil, eggs, Greek yogurt/sour cream and vanilla and continue mixing on low until smooth.
In a separate bowl, whisk together the flour, baking soda, and salt. Add the dry ingredients to the wet ingredients and mix just until combined. Stir in the chopped walnuts, if using.
Pour the batter into the prepared pan and bake for 45 to 50 minutes, until a toothpick inserted in the center comes out clean. Cool in the pan for 15 minutes, turn out onto a cooling rack, and cool completely.
Making the Cream Cheese Frosting
Yield: frosting for topping 1 9-inch cake
Using a mixer, mix together the cream cheese, butter, and vanilla on low speed until just combined. Add the powdered sugar and mix until smooth and creamy.
Spread the frosting on top of the cake and decorate with walnut and pecan halves, if using.