1. Preheat the oven to 375 degrees. Line 12 large muffin cups with paper liners. Place the oats on a rimmed baking sheet and lightly toast. Set aside to cool.
2. Combine the oats, flour, baking powder and salt in a large bowl and stir to mix. Whisk together the butter, eggs, bananas, buttermilk and oil in a separated bowl and blend well. Combine the two mixtures and stir just until all the dry ingredients are moist. Stir in the chocolate chips.
3. Scoop the batter into the prepared muffin tin with a large ice cream scoop ( 1/3 cup scoop).
4. Place in the oven to bake 25 to 30 minutes, until the tops of the muffins spring back when touched. Remove from the oven and let cool slightly. Serve warm.