Preheat the oven to 400 degrees. In a large bowl, toss the apples, sugar, 1/3 cup flour, the orange juice and zest, the cinnamon, 1/2 tsp. salt and the vanilla seeds.
Fit the piecrust into a 9-inch pie pan; crimp the edges. Transfer the apples to the crust; cover the pie loosely with foil and bake for 30 minutes.
Meanwhile, in a food processor, pulse the gingersnaps, remaining 1/4 cup flour and 1/4 tsp. salt until finely ground; transfer to a medium bowl. Using your fingers, blend in the butter until the mixture resembles wet sand.
Remove the pie from the oven and reduce the temperature to 350 degrees. Sprinkle pie with the candied ginger and the gingersnap mixture, cover with foil and bake until the apples are tender and the juices bubble, about 30 minutes. Let cool on a rack. Sprinkle with confectioners' sugar before serving.