Preheat oven to 180 C (355 F) and line a baking tray with baking paper.
Mash banana in a bowl.
Add egg, vanilla and cinnamon and whisk to combine.
Add flour and mix until well combined. Depending on the size of the banana, you may need to add more flour until mixture becomes a thick dough.
Place dough on a lightly floured surface and roll flat with a rolling pin (dust rolling pin with flour to keep it from sticking).
Cut out circles with a small cookie cutter.
Place circles on baking tray, evenly spaced, and gently press them down with a fork.
Bake for 10 mins.