Preheat the oven to 350°F (180°C) and prepare a muffin mold with muffin liners. Make sure you grease the liners to prevent the cupcakes from sticking.
In a large bowl, start by mashing the ripe bananas. When mashed, add in the egg, the peanut butter and whisk well until everything is well combined.
Sift in the protein powder and the baking powder, then whisk the ingredients until you get a smooth muffin batter. Do not overmix. Based on the type of protein powder used, you may need to adjust with up to 2 tbsp of milk if the batter is too dry (see notes*).
Fold through the chocolate chips.
Divide the batter evenly between the muffin cups and top with more chocolate chips, if you desire.
Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Let cool over a baking rack before serving.