Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a large bowl, mash the bananas until smooth.
Stir in the peanut butter until fully combined.
Add the oats and mix until everything comes together into a thick dough.
Gently fold in the blueberries.
Scoop spoonfuls of the dough onto the baking sheet and flatten them slightly into cookie shapes.
Bake for 12-15 minutes, or until the edges are golden and the cookies feel set.
Let them cool on the pan for a few minutes before moving to a wire rack.