Preheat oven to 350 degrees F. Spray 9" nonstick loaf pan with cooking spray. Set aside.
In a food processor or blender, add the 1 cup of old fashioned oats. Process until the oats are half their size or less. Add in brown sugar, flour, salt, baking soda, baking powder, and cinnamon. Pulse to combine. Dump dry mixture into a large bowl.
In a food processor or blender, add the bananas. Process until smooth. Add eggs, vanilla, and oil. Pulse to combine. Pour the wet mixture into the dry mixture. Fold in until just combined. Fold in the walnuts, if using.
Pour into prepared pan and bake for 45 - 50 minutes, or until a tester comes out clean. Cool in pan, on rack, for 10 minutes, then cool on rack. Wrap tightly with foil or plastic wrap and store in cool, dry place or in refrigerator. The flavor tends to get better the next day.