In a large mixing bowl, mash the peeled bananas either with a hand mixer, a fork, or a potato masher. When they are lightly mashed, add the sugars, oil, milk, vanilla, and egg to the bowl with the mashed bananas. Use a hand mixer to mix together until everything is combined evenly.
In a separate bowl, whisk together the flour, baking powder and salt. Pour the dry ingredients into the wet ingredients in 2 to batches, mixing quickly with a hand mixer to combine.
Fold in the blueberries and walnuts when the battery is ready.
Prepare a loaf pan by spraying with non-stick spray and then pour the batter to 2/3-3/4s full. If you have too much batter, split between two smaller loaf pans.
Place the loaf pan in the oven on the middle rack and bake for 55 to 65 minutes or until a toothpick stuck in the middle comes out clean.