For the Streusel:
In a medium bowl, combine the flour, sugar and cold butter pieces. Using a pastry cutter, fork or fingers, crumble together into a shaggy dough.
Combine with the walnuts and half of the candied ginger. Set aside the streusel and reserved ginger.
For the Pie:
Preheat the oven to 425 degrees.
In a large bowl, combine the pumpkin, apple butter, sugar, salt and Pumpkin Pie Spice, making sure all lumps are removed from the brown sugar. Stir in the eggs, and then gradually add the evaporated milk.
Transfer the pie filling into the crust and top evenly with the streusel. Bake for about 40 minutes, or until set.
Transfer to a cooling rack and top with the remaining ginger for a sparkling finish.