Preheat the oven to 180°C fan/400°F/gas 6. Line a large baking tray with non-stick baking paper.
In a blender or food processor blend 45g of the rolled oats into a flour.
To make the flax ‘egg’, put the ground flax seeds and water in a small bowl and leave to coagulate for 5 minutes or so.
Put the oats and oat flour into a large bowl, add the baking powder, salt, and coconut sugar.
Put the nut butter, 2 tbsp of water and vanilla into a bowl and mix well, until fully combined. Add into the dry ingredients along with the flax ‘egg’ and mix really well – this is easiest done by hand. Add the chocolate chips and bring together into a dough.
Weigh out 60g of dough for each cookie (you should get 7 cookies), then roll into a ball. Place the cookies on the lined baking tray with enough room between them for them to spread during cooking. Pat each one down flat with the palm of your hand, and add a few extra chocolate chips on top for decoration.
Bake in the preheated oven for 12 to 14 minutes, until they start to turn golden but before they start to burn. Allow to cool on the tray for 5 minutes, then transfer to a wire rack and allow to cool fully.