Heat Oven To 350 F. In A Large Bowl, Combine Cake Mix, Margarine And Egg. Mix At Low Speed Until Crumbly. Press Into Bottom Of Ungreased 9 X 13 Pan. Bake At 350 F. For 12 To 15 Minutes. Cool Completely. Spread 3/4 Cup Frosting Over The Crust, Reserving The Remaining Frosting For Later Use. Arrange The Bananas In A Single Layer Over The Frosting. Dissolve Gelatin In Boiling Water. In A Large Bowl Combine Dissolved Gelatin And Frosting. Beat Until Well Mixed. Add Cream Cheese And 1/3 Of The Whipped Cream. Beat Until Smooth. Spread Evenly Over The Bananas. Top With The Remaning Whipped Cream. Refrigerate For At Least 6 Hours Before Serving.