Preheat oven to 325°F. Mix wafer crumbs, chopped pecans, and butter in 13 x 9-inch baking dish. Be sure crumbs are moistened well and press firmly onto bottom of dish. Bake 15 minutes or until lightly golden brown. Let crumb mixture cool for at least 10 minutes. Top crumb crust with banana slices.
In large bowl, add Ensure Powder, pudding mix, and milk. Beat with wire whisk until well blended. Spoon half of the pudding mixture over the banana layer. Stir 1 cup of whipped topping into the remaining pudding mixture and pour over banana slices. Refrigerate for 3 hours. Serve with a dollop of whipped topping. Store leftovers in the refrigerator.