Chill two medium mixing bowls and the beaters of an electric mixer.
For crust, combine finely crushed cookies, 2 tablespoons sugar, and the melted butter or margarine in a small bowl. Press onto the bottom of an 8x8x2-inch baking pan. Chill crust while preparing filling.
Place ice cream in a chilled medium bowl; stir to soften. Stir in banana and walnuts. Pour into crust; cover and freeze about 6 hours or until firm.
Combine whipping cream and 1 tablespoon sugar in the other chilled bowl. Beat on medium speed until soft peaks form (tips curl). Spread over ice cream layer. Sprinkle shaved chocolate over whipped cream layer; freeze until firm (about 1 hour) or for up to 24 hours. To serve, place pan on a warm, damp cloth for a few minutes to loosen crust; cut into squares. Makes 9 servings.