Cream butter and sugar with a mixer until smooth. Add eggs, mashed banana, buttermilk, and vanilla. Mix until combined. Add flour, baking powder, salt and baking soda. Mix until combined. Stir in chocolate chips.
Spray a lined muffin tin with cooking spray. Add batter to cups and fill about 2/3 full. Bake for 20 minutes or until toothpick comes out clean.
For the Glaze:
Combine peanut butter, powdered sugar and water in a bowl. Mix with spoon until smooth. You can add more water if you prefer it to be thinner.