Spoon rhubarb evenly into a lightly greased 11- x 7-inch baking dish; sprinkle with 2 tablespoons sugar. Top with berries and apple. Set aside.
Combine oats and next 3 ingredients; cut in butter with a pastry blender until crumbly. Sprinkle over fruit mixture.
Bake at 375° for 25 minutes or until topping is browned and fruit is bubbling. Serve warm with cream, if desired.