Preheat: First, preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.
Mash: Next, in a large bowl, mash the bananas thoroughly with a fork until smooth.
Mix: Stir in the peanut butter and cinnamon until combined.
Combine: Then, add the oats and mix until a thick dough forms. Fold in chocolate chips if using.
Shape: Scoop the dough onto the baking sheet (about 12 cookies). Use the back of a spoon to flatten them into round cookie shapes.
Bake: Finally, bake for 12-15 minutes until set and lightly golden on the bottom. Cool for 5 minutes before eating.