Preheat the oven to 160C/Gas 2; grease a 35cm x 25cm baking tin and line with baking parchment
Mix together the oats, flour, cinnamon, butter, salt, vanilla and half the sugar substitute until very well and evenly combined
Place 2/3 of the oat mixture into the tin and press down lightly; keep the remaining 1/3 for the topping
Blend the fruit, the rest of the sugar substitute, the orange juice, orange rind and cornflour until well combined
Spread the fruit mixture over the oat base and add ½ the pistachios; sprinkle the remaining oat mixture and pistachios over the top
Bake for 35-40 minutes until golden; cut into squares while warm then cool completely before serving
24 servings