Combine flax crunch and brown rice flour in a medium sized bowl. Cut in butter. Stir to get ingredients well mixed.
For the Crust
Preheat oven to 375°F (190°C).
Put potato starch, tapioca flour, brown rice, hazelnut meal, powdered sugar in food processor. Pulse a few times to combine. Add butter and sugar. Pulse again until mixture resembles coarse bread crumbs. Add half-and-half and pulse again until a sticky dough forms.
Turn dough onto a large sheet of wax paper. Knead gently until dough holds together. At this point, dough is sticky but pliable. Place another sheet of wax paper on top of dough. With a rolling pin, roll dough into a 12-inch circle.
Peel off the top layer of wax paper. Invert onto a 10-inch pie dish, patching if needed. Trim and crimp edges as desired. Prick side and bottom with a fork.
Line crust with double layer of foil and bake for about 15 minutes. Remove and reduce oven temperature to 350°F (180°C).
Putting it together
Combine all filling ingredients in a large bowl. Mix well. Spoon into pie crust. Sprinkle crumb topping on top of fruits.
Bake in 350°F (180°C) oven for 50 to 55 minutes. Remove and allow pie to cool.