HEAT oven to 425 degrees F. Whisk together pumpkin, sweetened condensed milk, egg, 3/4 teaspoon cinnamon, ginger, nutmeg and salt in large bowl. Pour into crust.
BAKE 15 minutes. While pie is baking, combine brown sugar, flour and remaining 1/2 teaspoon cinnamon in small bowl; cut in butter with pastry blender or 2 knives until mixture resembles coarse crumbs. Stir in nuts.
REMOVE pie from oven; reduce oven to 350 degrees F. Sprinkle streusel mixture over pie.
BAKE 40 minutes or until set. Cool. Serve warm or at room temperature. Top with whipped cream, if desired.