Preheat oven to 350. Lightly oil a bread pan.
Combine flour, sugars, baking powder, baking soda, salt and cinnamon.
Combine oil, eggs, buttermilk, vanilla, and mashed bananas.
Pour liquid ingredients into dry ingredients. Stir gently to combine. Add walnuts, if desired. Pour batter into bread pan.
Bake 45-60 minutes. Check for doneness with a toothpick inserted into the center. When it comes out clean, the bread is done. Cool in the pan on a rack. Run a knife around the inside of the pan before removing bread. Tap the bottom if it doesn’t come right out.