Preheat the oven to 350F and line a baking sheet with parchment paper.
Make the batter:
In a medium bowl, mash the bananas with a fork. Add the applesauce and vanilla, stir to combine. Mix in the old-fashioned oats and thoroughly combine until you have a thick batter.
Gently fold in the blueberries.
Make the cookies:
Using a cookie scooper or large tablespoon, scoop the batter onto the lined baking sheet, gently press the dough with the back of the scoop or spoon, to flatten the cookies.
Bake:
Transfer the baking sheet into the preheated oven and bake for 20 to 25 minutes or until the cookies are a light, golden brown.
Notes
*You can substitute applesauce for 1 egg + 1 tablespoon of water.