Preheat the oven to 350 degrees. Place pie crust in an 8-inch pie pan. Combine pumpkin, coconut milk, sugar, cornstarch, cinnamon, ginger, salt, and allspice in a powerful blender or food processor until smooth. Pour mixture into pie shell and bake for 60-70 minutes. Remove from the oven and place on a cooling rack until completely cooled. Cover in plastic wrap and refrigerate for at least four hours (overnight is better) before serving. Garnish with vegan whipped topping and powdered sugar.