Preheat oven to 425. To make the fruit: In a medium saucepan, stir together the sugar and cornstarch. Stir in the water and orange juice.

Cook and stir over medium-high heat until the mixture is thickened and bubbly.

Add the rhubarb pieces; cook and stir until the mixture returns to boiling. Remove from heat. Cover the mixture to keep it warm.

To make the dumplin's: In a medium bowl, stir together the all purpose flour, rolled oats, sugar, whole wheat flour, and baking powder. In a small bowl, stir together the milk and cooking oil.

Add the milk mixture to the flour mixture; stir just until the flour mixture is moistened. Do not overmix.

Transfer the warm rhubarb mixture to a 13x9x2 inch baking pan or a 2 quart casserole dish. Immediately spoon the dumpling batter into 8 mounds on top of the warm rhubarb mixture.

To make the topping: In a small dish, stir together sugar and cinnamon. Sprinkle the sugar over the top of the dumplin's.

Bake, uncovered, in the 425 oven about 20 minutes or until done. Test for doneness by lifting a dumplin' to see if it's done underneath. Serve warm.