Preheat your oven to 350°F (175°C) and lightly grease a 9x13-inch baking dish.
In a large bowl, combine the rolled oats, baking powder, cinnamon, and salt. Mix well.
In another bowl, whisk together the milk, maple syrup (or honey), applesauce, and eggs until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined.
Fold in the diced apples, nuts, and dried fruit if using.
Pour the mixture into the prepared baking dish, spreading it evenly.
Bake for 30-35 minutes or until the top is golden brown and the oatmeal is set.
Allow to cool for a few minutes before slicing and serving. Enjoy warm or at room temperature.