Preheat oven to 350°F and lightly grease a pie dish with coconut oil.
Prepare flax egg: add flaxseed and water to a small bowl. Stir to combine. Let sit 5 minutes, or until thickened.
To a high-speed blender or food processor, add walnuts and rolled oats. Blend until broken down into a fine flour. Pour flour into a large bowl and add egg or flax egg, maple syrup, coconut oil, sea salt, and vanilla extract. Stir to combine. Reserve 1/3 cup dough to sprinkle on pie in a bit.
Press crust mixture into the bottom and slightly up the edges of greased pie pan. Bake pie crust for 10 minutes.
While pie crust pre-bakes, add berries to a bowl. Add cornstarch or potato starch and coconut sugar. Stir to combine. Pour berry mixture into pre-baked pie crust. Sprinkle remaining crust mixture on top. Return to oven and bake for an additional 35-40 minutes or until crust is golden and berries and slightly bubbling.
Remove pie from oven and let cool slightly before serving. Enjoy with your favorite vanilla ice cream – enjoy!