Preheat oven 350 degrees. In a large bowl add berries, and toss evenly with tapioca starch. Gently stir in maple syrup, lemon juice, and vanilla. Set aside.
Using a food processor, add walnuts, and pulse until finely ground.
Transfer to a medium bowl, then add coconut flour, sugar, vanilla, coriander and salt.
Add pieces of coconut oil, and cut into mixture using a knife or pastry cutter until mixture comes together.
Sprinkle topping over fruit and bake for 25 minutes, or until golden brown. It is delicious served with ice-cream or whipped coconut cream.