In a small bowl, combine the graham cracker crumbs and the melted butter. Set aside 1/2 cup of the mixture, then press the remainder into the bottom of a 9- by 13-inch pan.
Place the bananas in a single layer over the crust. Spread the softened ice cream on top and smooth. Sprinkle the nuts on the ice cream, then cover with plastic wrap and freeze until firm, about 1 hour.
In a large saucepan, melt the chocolate chips and the remaining 1/4 cup butter and stir until smooth. Add the confectioners’ sugar and evaporated milk. Cook, stirring constantly, over medium heat until slightly thickened and smooth, about 8 minutes. Remove the pan from the heat and stir in the vanilla. Cool the mixture, about 30 minutes, stirring occasionally. Pour the mixture over the ice cream and freeze until firm, about 45 minutes.
Spread the whipped topping over the chocolate layer and sprinkle with the reserved crumbs. Freeze for at least 3-1/2 hours. Remove the dish from the freezer 10 to 20 minutes before slicing. Serves 18.