Filling: In large bowl, combine sugar, flour, cinnamon and orange rind. Add rhubarb and strawberries; toss well. Spread mixture in 13 x 9 in. (3.5 L) baking dish. Bake in 400F(200 °C) oven 10 minutes. Topping: In large bowl, combine flour, sugar, baking powder, baking soda and salt. Using fingers or two knives, cut in margarine until mixture resembles small peas. With fork, stir in buttermilk just until soft dough forms. Drop by tablespoonfuls in 12 mounds on top of hot fruit filling. Bake in 400F(200 °C) oven 25 minutes or until topping is golden brown and has risen.