Preheat the oven to 350ºF and have a 9-inch pie plate ready. To make the crust, process the hazelnuts until coarsely ground in a food processor. Add in the oil, maple syrup, salt, oat flour, and oats, and process again until the dough comes together. The dough should stick together slightly when pressed between your fingers. If it's too dry, try adding 1 teaspoon water or processing it a bit longer.
Transfer the dough to the base of the pie dish. Starting from the middle, press the mixture firmly and evenly into the dish, moving outward and upward along the side of the pie dish. The harder you press the crumbs into the dish, the better the crust will hold together. Bake uncovered until lightly golden, about 15 to 20 minutes at 350ºF.
To make the filling, drain and rinse the cashews. In a high-speed blender, combine the soaked cashews, maple syrup, oil, cocoa powder, melted chocolate, vanilla, and salt. Blend on high until the filling is completely smooth. It can take a few minutes of blending to get it smooth, depending on your blender. If the blender needs more liquid to get it going, add a tablespoon or more of water, as needed, to help it along.
Pour the filling into the prepared crust, scooping every last bit out of the container. Smooth out the top evenly. Place the pie dish on a flat surface in the freezer, uncovered. Freeze for 1-2 hours, and then cover the dish and transfer it to the fridge until ready to serve.
Slice and serve the pie chilled, with your favorite garnishes, like coconut whipped cream and shaved chocolate. I find that it's easier to cut into this pie when served from the fridge, but keep in mind that it will become softer if it's left at room temperature for too long. Store leftovers in an airtight container in the fridge for up to 1 week, or in the freezer for up to 3 months.