Combine first 8 ingredients in a bowl; cut in margarine with a pastry blender until the mixture resembles coarse meal. Add dates; toss well. Add yogurt and egg whites, stirring just until dry ingredients are moistened (dough will be sticky).
Turn dough out onto a lightly floured surface; with floured hands, knead lightly 3 to 4 times. Pat dough into an 8-inch circle on a baking sheet coated with cooking spray. Cut dough into 10 wedges, cutting into but not through dough. Bake at 350° for 25 minutes or until loaf sounds hollow when tapped.