In medium saucepan, combine rhubarb, 1/2 cup sugar and orange peel; mix well. Cook over medium heat for 8 to 10 minutes or until rhubarb is tender, stirring occasionally. Cool slightly. Stir in strawberries.
Heat oven to 450°F. Spray cookie sheet with nonstick cooking spray. In medium bowl, combine flour, 1 tablespoon sugar and baking powder; mix well. Using pastry blender or fork, cut in margarine until mixture resembles coarse crumbs. Add milk; stir just until all dry ingredients are moistened. Drop dough by about 1/4 cupfuls onto sprayed cookie sheet; flatten slightly.
Bake at 450°F. for 9 to 12 minutes or until light golden brown. Immediately remove from cookie sheet. Split shortcakes; place 2 halves on each individual dessert plate. Spoon about 1/3 cup topping over each shortcake.