Preheat the oven at 180 degrees Celsius for 15 minutes. Line a baking tray with a greased parchment paper.
Powder 1 cup oatmeal in a grinder. Keep the rest aside.
Mash ripe banana in a mixing bowl. Add apple sauce, and whisk well. Add cinnamon and vanilla extract. Mix.
Add the oatmeal flour and remaining oatmeal to the wet ingredients.
Mix everything together using a fork or a spatula. The mixture will be slightly crumbly and dry in appearance.
Spoon onto a parchment lined baking tray. Press slightly so that the cookies cook evenly.
Bake for 15-17 minutes. Allow to cool down before transferring it to air tight container.