Preheat oven to 300 degrees F if using a silver 9-inch springform pan (or to 275 degrees F if using a dark nonstick 9-inch springform pan). Reserve 16 of the pecan halves for garnish. Finely chop remaining pecans; mix with graham crumbs, sugar and margarine. Press firmly onto bottom of pan.
Beat cream cheese in large bowl with electric mixer on medium speed until creamy. Gradually add sweetened condensed milk, beating until well blended. Add chocolate and 1 tsp. of the vanilla; mix well. Add eggs, 1 at a time, mixing on low speed after each addition just until blended. Pour over crust.
Bake 1 hour or until center is almost set. Run knife or metal spatula around rim of pan to loosen cake; cool before removing rim of pan. Refrigerate 4 hours or overnight.
Mix pie filling and remaining 1 tsp. vanilla; spoon over cheesecake. Top with whipped topping and reserved pecans. Cut into wedges to serve. Store leftover cheesecake in refrigerator.