In a medium mixing bowl stir together flour, sugar, baking powder, and cinnamon. Cut in margarine until mixture resembles coarse crumbs. Make a well in center. Combine egg white, milk, and vanilla; add all at once to flour mixture. Stir until dough clings together.
Lightly coat a 9-inch pie plate with nonstick spray coating. With floured fingers, press batter evenly into pie plate. Bake in a 350 degree F. oven for 20 to 25 minutes or until golden. Cool slightly.
Meanwhile, chop 2 peach slices and stir into the yogurt. Arrange remaining peach slices over top of shortcake. Spoon yogurt mixture over all. Serve warm. Makes 10 servings.