Arrange the rhubarb in an oiled 8-inch baking dish. Combine sugar, flour grated orange peel and cinnamon; sprinkle over rhubarb. Sift together flour, baking powder, salt and sugar. Make a well and put in the butter. Cut the dry ingredients together with the butter, until mixture is crumbly. Mix egg and milk into flour mixture, just until moistened. Spread over rhubarb. Bake at 350 degrees for 25 minutes. Meanwhile, mix sugar and orange juice. Remove cake and pour orange juice over it. Continue baking 15 minutes longer. Turn cake upside down onto serving plate. Serve warm. Serves 8