01 - Preheat oven to 350°F (175°C). Grease a 9x9-inch baking dish with butter or nonstick spray.
02 - In a large mixing bowl, combine rolled oats, chopped nuts if using, baking powder, ground cinnamon, ground nutmeg, and salt until well incorporated.
03 - In a separate bowl, whisk together milk, eggs, melted butter or coconut oil, maple syrup or honey, and vanilla extract until smooth.
04 - Add the wet mixture to the dry ingredients. Stir gently until thoroughly combined. Fold in diced apples and dried fruit if desired.
05 - Pour the batter into the prepared baking dish and spread evenly with a spatula.
06 - Place dish in the oven and bake for 35 minutes, or until the top is golden and the center is set.
07 - Allow oatmeal bake to cool for 5 minutes before slicing. Serve warm with additional milk or yogurt if desired.