In a mixing bowl, combine sliced apples and vanilla. Toss to combine, set it aside.
Combine sugar, nutmeg, cinnamon and oatmeal in a bowl. Cut in the butter (click for How to Cut in Butter).
Add walnuts and mix well.
Preheat oven to 360 degrees F. Place apples in a baking dish and sprinkle oatmeal mixture over apples.
Bake for about 45-55 minutes or until topping looks crunchy and apples are tender.
Serve cold or hot.