Preheat oven to 375 degrees and line 12 muffin tins with papers.

In a large bowl, whisk together flour, oatmeal, baking powder baking soda and salt.  In a medium bowl, whisk together oil, brown sugar, eggs, banana, peanut butter and buttermilk until smooth.  The peanut butter will be a bit hard to incorporate, but be sure it is!

Pour wet mixture into flour mixture and fold with a rubber spatula just until flour is incorporated.  Do not overmix!

Fill muffin tins with the batter.  The tins will be very full, but they don’t rise all that much so it is ok.  Bake for 20 minutes until the top of a muffin springs back with lightly pressed.  Remove muffins from the pan and allow to cool completely.  Store in airtight container.  I find the flavors and texture improve if they sit overnight before serving.