Combine first 5 ingredients in food processor, and pulse until well-blended. With the processor on, drop margarine through food chute, and process for 10 seconds.
Combine buttermilk and egg whites; stir well. With the processor on, pour the mixture through food chute, and process for 20 seconds or until dough leaves sides of bowl and forms a ball. Turn the dough out onto a lightly floured surface, and lightly knead about 10 times.
Pat the dough into an 8-inch round cake pan coated with cooking spray, and cut a 1/4-inch-deep X in top of the dough. Bake at 375° for 45 minutes or until lightly browned. Remove bread from pan, and let cool completely on a wire rack. Cut bread into wedges.