Preheat your oven to 180°C (160°C fan-forced) and prepare two medium muffin tins with paper cases.
Finely chop the streaky bacon. Heat a non-stick frying pan over medium heat and add the bacon. Cook for 2-3 minutes or until the bacon starts to turn golden. Set it aside to cool.
Pour the contents of the banana bread mix into a large bowl, creating a well in the center. Add bananas, half of the cooled bacon, eggs, oil, and milk. Mix until well combined. Divide the mixture into paper cases in the prepared tins. Bake for 25-30 minutes or until lightly golden. Allow it to rest in the tins for 5 minutes before transferring to a wire rack to cool.
For the frosting, whip butter in an electric mixer until it becomes light and creamy. Slowly incorporate icing sugar, ensuring thorough beating after each addition. Introduce peanut butter and continue beating until the mixture achieves a light and fluffy consistency.
Scoop the frosting into a piping bag equipped with a large star nozzle, then pipe the frosting onto the cupcakes.
Finally, decorate each cupcake with the leftover pieces of bacon.