Pre-heat oven to 350 degrees and grease a 9x6 deep sided baking dish or 9x9 square dish with vegan butter, butter or coconut oil.

In a medium bowl mix together oats, baking powder, cinnamon, nutmeg, and salt. Set aside.

Peel, core and thinly slice apples.

Pour milk into a large bowl, crack eggs one by one into a smaller bowl, before adding to the milk bowl. Whisk eggs with the milk until well combined.

Add brown sugar and vanilla to milk mixture and continue to whisk until all sugar is dissolved.

Pour dry ingredients into the milk mixture and mix until well combined.

Line the bottom of baking dish with a layer of apples, pour about ¼ of mixture over the apples, continue to alternate layers of apples and oat mixture until you have used all oat mixture and apples.

Place topping ingredients in a small bowl mix together using the back of a fork or your fingers.

Sprinkle over oat mixture, bake oatmeal in oven 25 to 30 minutes or until top starts to turn golden brown.

During the last 15 minutes of cooking time, whisk brown sugar sauce ingredients in a small sauce pan until well combined. Heat pan over medium heat, stirring until mixture starts to thicken, about 3 to 5 minutes.

Transfer to serving dish and serve with oatmeal.