Bake pie shell.
Soften ice cream slightly; quickly fold in crystallized ginger.
Spread in pie shell.
Freeze until ice cream is solid.
Stir together pumpkin, sugar, pumpkin pie spice, ground ginger, salt and walnuts.
In chilled bowl, beat whipping cream until stiff; fold into pumpkin mixture.
Pour over ice cream in pie shell.
Freeze several hours.
Remove from freezer 10 to 15 minutes before serving.