Preheat the oven to 375°.
Add your bananas, eggs, sugar, and vanilla to a large mixing bowl. Mix until smooth.
Add in buttermilk, butter, and vegetable oil. Mix until well blended.
In a separate bowl, sift together flour, baking soda, salt, cinnamon, nut meg, and brown sugar.
Add lemon juice to your flour mixture.
Mix together the wet and dry ingredients. Blend until smooth.
Line a muffin tin with liners, and fill each one 1/4 of the way with batter.
In a small mixing bowl mix together all filling ingredients until smooth.
Add about one heaping teaspoon of filling to the center of each muffin tin, as shown.
Add more batter on top of filling until liner is 3/4 of the way full.
Sprinkle the top of your batter with crushed nuts if desired.
Bake for 14 minutes or until baked through.