Preheat oven to 425°F.
Combine pie filling, cranberries and walnuts; mix well. Spoon evenly into crust and place second crust on top.
Fold two crusts together; seal and crimp edges. Cut several slits in the top crust to allow steam to escape.
Bake for 35-40 minutes. Transfer to a wire cooking rack; cool completely.
Prepare icing by beating together butter, sugar and flour with electric mixer. Add milk, vanilla and cinnamon; beat well. Additional milk may be added to reach desired consistency. Spread icing evenly over cooled pie.