Preheat the oven to 375ºF. In a large bowl, whisk together the apple sauce, egg, brown sugar, vanilla, cinnamon, nutmeg, salt, baking powder, and melted butter. Once whisked smooth, add the milk and whisk until smooth again.
Add the raisins and dry rolled oats. Stir with a spoon until the mixture is combined. Lightly coat a 9x9 casserole dish (or any 2-3 quart casserole dish) with non-stick spray, then pour the oat mixture into the dish.
Bake the oatmeal uncovered in the fully preheated oven for 45 minutes. Divide into six portions and serve. Baked oatmeal is good warm or cold and tastes great with cold milk poured over top.