To prepare crust, combine crumbs, margarine, and sugar in a mixing bowl. Press mixture firmly in a 9" pie pan. Chill one hour, or until firm. Or, bake in a 350 oven for ten minutes or until lightly browned. Cool on rack before filling. Meanwhile,to prepare filling, combine cream cheese, sweetened condensed milk, 1/3 cup lemon juice, and vanilla extract in another mixing bowl. Line three bananas onto bottom of chilled crust. Turn filling into crust. Refrigerate for three hours or until firm. Dip remaining bananas in remaining lemon juice. Arrange banana slices over top of pie.