Preheat oven to 350°F (177°C). Line an 8 inch by 8 inch baking pan with parchment paper.
Add mashed bananas and rolled oats to a large mixing bowl. Mix until oats are fully coated and evenly mixed in. Add in blueberries. Gently stir them in until the are evenly mixed throughout, being careful to not smash the blueberries.
Pour batter into the prepared baking pan. Use a spatula to evenly spread it across the pan and smooth the surface.
Bake for about 20 minutes or until the oats on the surface are golden brown. The surface of the bars should look dry and cooked. Let bars cool fully before removing them from the pan and cutting and serving. Store uneaten bars in an airtight container in the fridge or freezer.
