Preheat oven to 350 degrees Fahrenheit. Lightly coat a loaf pan with non-stick spray.
In a medium bowl, mash bananas with a fork. Add butter and sugar and mix well. Add buttermilk, sour cream, eggs and vanilla and mix thoroughly.
In a separate bowl, combine baking soda, baking powder, salt, cinnamon and flour. Add dry ingredients to banana mixture and mix until combined. Fold in diced strawberries.
Pour batter into a greased pan and bake 55-60 minutes.