Preheat the oven to 375 degrees F. Coat a 12-cup muffin pan with non-stick cooking spray or line it with cupcake liners.
Place the oats on a rimmed baking sheet and transfer it to the oven for 3 to 5 minutes, or until lightly toasted. Set aside to cool.
Combine the oats, flour, baking powder and salt in a mixing bowl and stir to mix.
In a separate large mixing bowl, whisk together the sugar, buttermilk, and oil. Add the melted butter, lightly beaten eggs, and mashed bananas, and whisk to combine.
Add the dry mixture to the wet mixture and use a spoon to stir just until all the dry ingredients are moist. Stir in the chocolate chips.
Spray a 1/3 cup dry measure with non-stick cooking spray. Scoop out a heaping 1/3 cup of batter to fill each cup in your muffin pan. You may need to spray the measuring cup with additional non-stick cooking spray in between scoops if the batter begins sticking.
Bake for 25 to 30 minutes, until golden brown and the tops of the muffins spring back when touched. Remove from the oven and let cool slightly.
Delicious served warm or cold.