Preheat oven to 350 degrees. Spray a 9x5x3 loaf pan with nonstick spray and then line with parchment paper and spray that as well.
In a medium bowl, mix together the dry ingredients: flour, granulated sugar, brown sugar, baking powder, and baking soda.
In a large bowl, combine and beat on low speed the oil, sour cream, eggs, and vanilla. Add in mashed bananas and blend together.
A little at a time, add the dry ingredients to the wet and mix just until it's combined. Do not over mix.
In a small bowl, mix together the 2/3 cup sugar and 1 tbsp cinnamon.
Pour and spread 1/2 of the batter into the prepared loaf pan. Sprinkle all of the cinnamon sugar mixture over top.
Pour and spread the rest of the batter over the cinnamon sugar layer.
Sprinkle granola over the top of the batter in an even layer.
Bake for 60-70 minutes until toothpick inserted comes out clean.