Preheat the oven to 350° F. Put the cake mix, eggs, olive oil, water, bananas, oatmeal, walnuts and vanilla extract into a large mixing bowl and stir until they are well incorporated. Next, fold the blueberries gently into the batter so you don’t bruise them. Spray a 9" loaf baking pan with nonstick cooking spray. Pour the mixture into the pan, sprinkle the granulated sugar evenly over the top of the loaf and then place into the oven for 1 hour and 25 minutes. The bread should be golden brown when it’s ready.