Preheat oven to 350°F. Spray a 9” x 5” loaf pan with cooking spray.
In a large bowl, whisk flour, Splenda Sweetener, baking powder, baking soda, cinnamon, nutmeg, and salt until combined.
In another bowl, stir together mashed bananas, oil, buttermilk, and vanilla extract; mix well. Pour banana mixture into flour mixture and stir until just combined.
Mix in walnuts if using. Pour batter into prepared pan.
Bake for 45–55 minutes or until the center is set and the bread is deeply brown. Let cool before slicing.