Combine first 5 ingredients in a medium bowl; cut in margarine with a pastry blender until mixture resembles coarse meal. Add buttermilk, stirring with a fork just until dry ingredients are moistened.
Sprinkle 1/2 teaspoon flour evenly over work surface. Turn dough out onto floured surface, and knead 10 to 12 times. Shape dough into a 3-inch round; place round on a baking sheet coated with cooking spray. Cut a 1/4-inch-deep cross in the top of round with a sharp knife. Coat top of round with cooking spray. Bake at 425° for 8 to 10 minutes or until golden.