Butter a 9x13-inch pan. In a medium bowl, combine cookies and margarine. Toss to coat crumbs with margarine. Press evenly over bottom of prepared pan. In a small bowl, sprinkle banana slices with lemon juice, and toss lightly to coat slices thoroughly to prevent darkening. Set aside. Stir vanilla ice cream to soften slightly. Spread ice cream over prepared crust. Drizzle with fudge sauce. Freeze until almost firm. Top with banana slices. Stir strawberry ice cream to soften slightly, and spread over bananas. Freeze until firm. To Serve. Top with lightly sweetened whipped cream and a drizzle of Thick Fudge Sauce. Serves 15 to 18. Thick Fudge Sauce. In the top of a double boiler, combine chips and cream. Heat over simmering water until chips melt and blend thoroughly with cream. Keep sauce refrigerated. Makes 2 cups. RICH, rich, rich...but good, good, good!! Wis/Gramma