Place oven rack on lower third shelf and preheat to 350 degrees Fahrenheit (176 degrees Celsius). Grease a 9×9 inch or 11×7 (which is the one I use) baking pan.
Whisk all ingredients together in one bowl. Combine the ingredients for the filling in a separate bowling. Pour half of the oatmeal mixture into the pan and sprinkle half of the filling over it. Then pour the remaining oatmeal on top and sprinkle the rest of the filling on top.
Bake for 35 minutes or until center seems almost set. While baking, mix together the ingredients for the frosting.
Cool for 5 minutes before serving. Spread desired amount of frosting on top.