Preheat oven to 375℉. Spray a 9×9-inch baking dish with cooking oil spray.
In a bowl, combine all of the ingredients.
Transfer to the prepared 9×9-inch dish. Top with a few additional frozen berries, if desired.
Bake for 30 minutes or until the center is just set. For a more firm, bar-like, oatmeal bake, bake for 33-35 minutes.
Let set for 5 minutes before serving.
