Preheat the oven to 350°F (175°C). Line a baking pan with parchment paper.
In a bowl, smash the blueberries using a fork. Combine with the maple syrup and arrowroot powder. Set aside.
Add half the oats to a food processor or blender to create oat flour.
Transfer to a mixing bowl and combine with the remaining rolled oats, banana, and water.
Firmly press ¾ of the oats mixture into a thin, even layer in the baking pan. Spread the blueberry mixture on top and then crumble the remaining oat mixture over the blueberries.
Bake for 20 to 25 minutes or until golden brown.