Begin by placing the ground flaxseed in a bowl with the warm water. Give it a stir then set aside.
Mash the banana with a fork.
Then, in a large mixing bowl, add the ground oats, flour, baking powder, mashed banana, and the flaxseed/water mixture.
With a fork or wooden spoon, stir the mixture thoroughly until a dough forms. You might need to add more or less flour to make sure the dough isn’t sticky. It should be soft but not sticky.
Preheat the oven to 170°C/350°F and line 1-2 baking trays with parchment paper.
Next, dust your clean work surface and rolling pin with some plain flour.
Tip out the dough onto the work surface and sprinkle over some more flour if the dough is too sticky.
Roll out the dough to 0.5cm thickness.
Next, using your favourite cookie cutter, cut out as many shapes as possible from the dough.
Transfer the cookie shapes onto the prepared trays.
Re-roll the dough and keep making shapes until all the dough is used up.
These cookies don’t spread, so you’re fine to pack them about 1cm apart on the baking tray.
Bake in the oven for 15-17 minutes or until lightly golden.