Bake the pie crust according to the package directions and allow it to cool.
In the top of a double boiler over low heat, combine the marshmallows and the pumpkin puree. , Stir constantly, with a heatproof spatula, until the marshmallows are melted. Take the pan off the heat and stir in the spice and salt.
When the mixture is completely cool, stir in half of the whipped topping. Pour the filling into the prepared pie crust. Top with the remaining whipped topping and garnish with cinnamon.