01 - Preheat the oven to 350°F. Lightly grease a 9x9-inch baking dish with butter or non-stick spray.
02 - Combine rolled oats, nuts, baking powder, ground cinnamon, nutmeg, and salt in a large mixing bowl.
03 - In a separate bowl, whisk together milk, eggs, melted butter, maple syrup, and vanilla extract until fully blended.
04 - Pour the wet mixture into the bowl with the dry ingredients. Stir gently until evenly incorporated.
05 - Fold in the diced apples and raisins or dried cranberries until distributed throughout the mixture.
06 - Spread the oatmeal mixture evenly into the prepared 9x9-inch baking dish.
07 - Bake at 350°F for 35 minutes, or until the top is golden brown and the center is set.
08 - Allow to cool for 5 minutes before slicing and serving warm. Optionally top with extra milk or a spoonful of yogurt.