Preheat the oven to 200°C (Gas Mark 6 / 400°F).
Add the mashed bananas to a stand mixer, and add the sugar, yogurt, egg and peanut butter. Mix until smooth. Add the cinnamon, baking powder, flour and chocolate chips, and use a plastic spoon or spatula to fold the mixture together until just combined.
Grease a 12-cup muffin tray, and distribute the mixture between the cups, filling each nearly to the top. Dot a few more chocolate chips on top of each, if you want the chocolate chips to be particularly visible in the finished muffins.
Bake the muffins for around 10 minutes, then turn the oven down to 180°C (Gas Mark 4 / 350°F). Cook for a further 10 minutes, or until a toothpick inserted into the middle of a muffin comes out clean.