Combine crushed cookie crumbs, pecans, and butter or margarine. Press into a 9 x 13 inch pan. Bake at 375 degrees F (190 degrees C) for 5 minutes. Cool.
Combine chocolate chips, 1 cup milk and 2 cups marshmallows in a saucepan. Stir over low heat until melted. Pour over cooled crust. Chill for 1 hour.
Arrange banana slices over chilled chocolate layer. Prepare pudding mix as directed on box except use only the remaining 3 cups of milk. Fold in nondairy whipped topping and remaining marshmallows. Pour pudding mixture over bananas. Grate chocolate bar over the top. Chill for 2 to 3 hours before serving.