01 - Preheat oven to 350°F (175°C). Grease a 9x9-inch baking dish with nonstick spray or butter.
02 - In a large mixing bowl, combine rolled oats, chopped nuts, baking powder, ground cinnamon, ground nutmeg, and salt. Stir thoroughly to distribute the spices and leavening agent evenly.
03 - In a separate bowl, whisk together milk, eggs, melted butter, maple syrup, and vanilla extract until fully blended.
04 - Pour the wet mixture over the dry ingredients. Stir until all components are just combined. Gently fold in diced apples and dried fruit, if using.
05 - Spread the oatmeal mixture evenly into the prepared baking dish, ensuring fruit is distributed throughout.
06 - Bake in the center of the oven for 35 minutes, or until the top is golden and the oatmeal is set at the center.
07 - Allow oatmeal bake to cool in the dish for 5 minutes before slicing and serving. Enjoy warm, with additional milk or yogurt if desired.