Preheat the oven to 350 degrees. Coat a 9-inch springform pan with nonstick cooking spary. In small bowl, mix together the vanilla wafer crumbs and margarine and pat into the bottom and up sides of a 9-inch springform pan. In another mixing bowl, beat together the cream cheese, sugar and cornstarch until creamy. Add eggs and egg white, one at a time, beating until blended after each addition. Add the mashed banana, sour cream, cinnamon, lemon juice, and vanilla, mixing until combined. Transfer the filling to crust lined pan. Bake for 1hour or until center of cake is just about set. Remove from oven and transfer the pan to a wire rack to cool completely at room temperature. Refrigerate until well chilled. To serve, top the cheesecake with walnuts and slice bananas, and drizzle with caramel sauce.