Preheat oven to 375°F. Line a 9-inch pie dish with pastry dough; turn under excess dough to fit dish and flute decoratively.
Whisk together pumpkin, brown sugar, milk, spices and eggs until smooth and pour into pastry.
Stir together streusel ingredients in a medium bowl with a fork and carefully sprinkle over pie.
Bake for 45 to 50 minutes, tenting with foil if crust browns too quickly. Let cool completely before serving.
For an extra ginger kick, top pie with a ginger whipped cream. Whip heavy cream with a little powdered sugar to lightly sweeten, then stir in finely chopped crystallized ginger to taste.