Preheat oven to 425F. Line muffin pan with baking liners.
In a large bowl, combine flour, baking powder, baking soda, cinnamon, and salt.
In a medium bowl, combine oil, white sugar, brown sugar, eggs, milk, vanilla extract, and bananas. Whisk together until well-combined.
Add wet ingredients to the flour mixture. Using a rubber spatula, gently stir together just until moistened. Do not over mix.
Gently fold in 1/2 of the chopped walnuts.
Scoop batter evenly into prepared muffin pan up. Sprinkle with the remaining ⅓ cup walnuts.
Bake at 425 F for 5 minutes. Reduce the heat to 375F and continue to bake for another 12 to 15 minutes or until a toothpick inserted in the middles comes out clean.
Allow to cool for about 1 to 2 minutes and transfer onto a cooling rack.