Preheat oven to 350F/180C.
To make the crust, combine the ground flaxseeds, applesauce, coconut sugar, and coconut oil in a bowl. Whisk until uniform. In another bowl, whisk together the oat flour, brown rice flour and tapioca flour. Add the wet ingredients to the dry and stir until you get a uniform soft dough. Refrigerate for 30 minutes.
Roll the dough out between two sheets of parchment paper, then transfer to a 9-inch pie dish. Using your hands, press the dough evenly into the bottom and sides of the dish. You can use a glass to flatten the bottom. Prick the dough a few times with a fork. Refrigerate until needed.
To make the crumble topping, combine the oat flour, brown rice flour, and coconut sugar in a small bowl. Whisk until uniform, then pour in the melted coconut oil. Rub the wet ingredients into the dry until you get a crumbly mixture. Set aside.
To make the filling, combine the wild blueberries, maple syrup, arrowroot. and lemon juice in a large saucepan. Bring the heat to medium-high and cook, stirring often, until you get a very thick mixture. Transfer filling to prepared crust and top with crumble. Bake for 25-35 minutes, until the crust is browned. Cool pie completely before serving.