Preheat Oven to 190c and line an 8x8 tin (or similar size) with baking paper
Mash the bananas in a large bowl until mostly smooth (a few lumps are okay)
Stir in the nut butter, flax eggs, cinnamon, pinch salt (if using), vanilla extract, baking powder, and maple syrup (if using)
Stir in the oats until well combined
At this point, you can stir in your add-ins (if using)
Add the mixture to the lined tin and spread out so it's even
Place in the oven to bake for 30 minutes, until the top is golden
Remove and leave to cool for a few minutes before slicing in to 12 bars
Store in an airtight container