Spray muffin pans or line with muffin papers. Set oven to 375°. Create buttermilk by stirring lemon juice into milk. Set aside while mixing ingredients.
In a medium bowl, combine flour, baking soda, baking powder, and salt. Stir in brown sugar. Set aside. In a small bowl, mix together quick oats and boiling water. Set aside.
Whisk egg and oil into buttermilk. Add quick oats to flour mixture. Stir in buttermilk, egg, and oil until muffin batter is creamy. Mash bananas and add to muffin batter.
Fill muffin tins 3⁄4 full with batter. Add a teaspoon full of Nutella into the center of each muffin. Stir in with a toothpick or cake tester. Bake for about 18 minutes.
Allow to cool for 5 minutes before removing to a wire rack. Use a knife to carefully remove the muffins. Allow muffins to cool completely before serving as the texture of the muffin is much