Add egg, vanilla extract and bananas and blend well.
Add remaining ingredients (except chips) and stir until well blended.
Gently stir in peanut butter chips.
Spoon batter into prepared pan and bake for 40 minutes, or until a toothpick inserted in the middle comes out clean.
Let cool for 15 minutes.
Meanwhile, make icing by combining butter and peanut butter in a microwave safe bowl and microwaving on 50% heat for about 30 seconds, or until just melted.
Stir the butters together until fully melted.
Stir in Allulose until well combined.
Add milk, one teaspoon at a time, until a smooth mixture is formed.