Preheat the oven to 180˚C/ 350°F/Gas Mark 4. Coat 2 large baking sheets with cooking spray. Then, in a large bowl, mix the rolled oats, flour, raisins, baking powder, cinnamon, nutmeg, and salt. Set mixture aside. In another large bowl, using a wooden spoon, mix the rapeseed oil into the brown sugar until well combined. Mix in the sweet potato purée, egg whites and vanilla extract. Then add the chocolate chips. Add the oats mixture all at once into the bowl with the oil and sugar. Stir until a thick dough forms.