Preheat oven to 375 degrees Fahrenheit. Prepare a muffin tin with non stick cooking spray or muffin liners. Set aside.
In a medium bowl, combine the flour, oats, white sugar, brown sugar, baking powder, baking soda and salt. Stir until combined.
In a large bowl beat the egg. Add milk, oil, vanilla, and mashed bananas. Stir to mix ingredients until well combined.
Add flour mixture to banana mixture and stir until just combined; do not over stir.
Divide batter evenly between 12 muffin cups. Fill each cup about ⅔ to ¾ full.
Add a generous teaspoon of peanut butter to top of muffin and cut into batter in a figure 8 pattern with a toothpick.
Bake at 375 degrees Fahrenheit for 17-20 minutes or until a toothpick inserted in the center comes out clean or with a few moist crumbs.