Preheat oven to 350°F (180°C) and line a 12-count muffin tin with muffin liners.
In a bowl, combine flour, baking powder, baking soda, salt, and cinnamon. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment combine butter and sugars. Beat at medium-high speed for about 4 minutes until pale and fluffy.
Add the egg and vanilla extract, whisk until combined. Stir in the mashed bananas.
Add the dry ingredients to the wet mixture and stir just until combined. Don't overmix!
In a small bowl combine peanut butter and powdered sugar. Mix until smooth.
Spoon about 1 heaping tablespoon of batter into each muffin cup. Place on heaping tsp of filling on top. Divide remaining batter between the muffin cups.
In a small pan over medium heat melt the butter. Then add chopped peanuts and maple syrup. Stir for about 1 minute then remove from heat. Top each muffin with a tsp of the topping.
Bake muffins for about 20-25 minutes or until a skewer inserted into the center comes out clean with only a few crumbs attached. Let the muffin cool down for about 10 minutes in the pan then transfer them to a cooling rack.