Adjust the oven rack to the lower third position and preheat the oven to 350°F (177°C). Spray a 9×9 inch or 11×7 inch baking pan with nonstick spray. Any similar size or shape pan works, though 8×8 inch would be too small. See recipe note for 9×13 inch pan.
Whisk all of the ingredients together in 1 large bowl. Pour into prepared baking pan. Top with nuts, if desired. (Or stir into the oatmeal.) Bake for 35 minutes or until the center appears
Cool for 5 minutes before serving. Spoon or slice and serve with yogurt, if desired. Cover leftovers tightly and refrigerate for up to 1 week.