Combine crumbs and margarine; press onto the bottom of a 23 cm springform pan. Bake at 180ºC ., 10 minutes. Combine cream cheese, sugar and banana, mixing at medium speed on electric mixer until well blended. Add eggs, one at a time, mixing well after each addition. Stir in walnuts, pour over crust. Bake at 180ºC ., 40 minutes. Loosen cake from rim;cool before removing rim pf pan. Melt chocolate pieces and margarine with water over low heat, stirring until smooth. Drizzle over cheesecake. Chill.