01 - Preheat oven to 350°F. Lightly grease a 9x9-inch baking dish.
02 - In a large mixing bowl, stir together rolled oats, chopped nuts, baking powder, ground cinnamon, ground nutmeg, and salt.
03 - In a separate bowl, whisk milk, eggs, melted butter, maple syrup, and vanilla extract until well blended.
04 - Pour wet mixture over the oat mixture and stir gently until thoroughly combined.
05 - Fold in diced apples and raisins or dried cranberries, ensuring even distribution.
06 - Transfer mixture to the prepared baking dish, smoothing the top with a spatula.
07 - Bake in the center of the oven for 35 minutes, or until the surface is golden and the oats are set.
08 - Let the baked oatmeal cool for 5 minutes before serving. Serve warm, optionally topped with extra milk or yogurt.