1. In a large bowl, stir together the gelatin and boiling water till gelatin is dissolved. Chill till partially set. Stir in strawberries, pineapple, bananas and walnuts.
2. Turn half of the mixture into a 3-qt. rectangular (13x9x2-in.) dish. Place in your freezer for 10 to 12 minutes or till firm. Spread with sour cream. Spoon remaining strawberry mixture over sour cream. Cover and chill for at least 4 hours or till firm.