If starting with oats, blitz them in a blender to form oat flour. Add to a large mixing bowl with the ground almonds.
Add the cold coconut oil or vegan butter/margarine to the bowl and use a knife to cut it into the flour. Now use your fingertips to rub the fat into the flour to form a sticky mix. Stir through the coconut sugar, cinnamon and salt. Pour in the cold water and bring the dough together with a spoon. Shape into a ball and cover in a wrap. Leave to chill in the fridge for 20-30 minutes.
Meanwhile, de-stone and slice the nectarines. Add to a small bowl with the blueberries, lemon juice, lemon zest, coconut sugar and cornflour. Stir well and leave to one side.
Preheat the oven to 170Fan/190*C. Cover a surface with a large piece of baking parchment and place the dough on top. Using a second piece of parchment, carefully roll the dough out between the two sheets to form an oval shape, ½ cm thick.
Spoon the fruit mixture (leave the juice in the bowl) into the centre of the dough, leaving a 2cm gap around the edge. Using the bottom sheet of parchment, roll/fold the edges of the dough over the fruit towards the centre – it is best to use the parchment to avoid tears in the pastry and to create a smooth edge.
Transfer the baking parchment and the pastry onto an oven-proof tray and bake for 40-50 minutes until golden and crisp.
Serve warm or cold with banana ice cream, yoghurt or on its own.