Whisk together the flour, salt, and sugar in a large bowl. Add the butter to the flour mixture and toss to coat. Using a pastry blender, cut the butter into the flour until only pea-sized pieces of butter (or smaller) remain.
In a separate small bowl, combine the water, cider vinegar, and ice. Sprinkle 2 tbsp of the ice water mixture over the flour-butter mixture. Toss with your hands until fully incorporated. Add more of the ice water, 1-2 tbsp at a time, using your hands to mix. Add just enough of the water mixture so that the dough comes together into a ball. Wrap in plastic wrap and refrigerate for at least 1 hour.
Roll out the pie disc into an 11-inch round. Use this to line the pie plate and crimp the edges as desired. Place in the freezer while you prepare the filling.
For the filling
Combine the cranberries, sugar, mandarin zest, salt, and cornstarch in a medium pot over medium heat. Cook until the cranberries start to release some juice, about 5 minutes. Then cook another 5 minutes more, stirring frequently until the filling has thickened and all of the cranberries have burst. Transfer to a bowl and allow to cool for 5-10 minutes.
For the crumble
Place the oats in the bowl of a food processor and grind until they form a powder. Add in the pecans and process until coarsely ground. Add in the flour, sugar, brown sugar, cinnamon, and sea salt. Pulse to combine. Add in the melted butter and pulse just until thick crumbs form. Set aside.
For the pie
Heat oven to 375F.
Pour the cranberry filling into the prepared pie crust and top with the crumble.
Place on a parchment- or foil-lined baking sheet and bake for 45-50 minutes, or until the juices are bubbling. Allow to cool to room temperature before serving.