Combine cracker crumbs and melted butter or margarine thoroughly and press into bottom of 9x12 inch baking pan. Chill in freezer for at least 15 minutes.
In the medium bowl of an electric mixer combine confectioners sugar, eggs, and softened butter or margarine; beat at medium speed for 20 minutes. (This step is important, so don't try to save time).
Spread buttercream mixture evenly over chilled crust. Place bananas, cut side down, evenly on top of buttercream and spoon crushed pineapple evenly over top of bananas. Distribute strawberries over pineapple and spread the whipped topping evenly all over. Sprinkle with walnuts and refrigerate for at least 3 hours or overnight before serving.