Preheat oven to 375 degrees F. Place the sliced apples in an 8x8 inch baking pan.
Whisk the maple syrup, 2 Tablespoons melted butter, vanilla, 1/2 teaspoon ground cinnamon and 1/4 teaspoon ground nutmeg together then pour over the apples and toss to coat.
In a separate mixing bowl, combine the oats, flour, brown sugar, salt and remaining cinnamon and nutmeg. Pour the rest of the melted butter over the mixture and combine it with a fork until the mixture is thoroughly coated.
Crumble the topping evenly over the apple mixture then bake it for about 40-45 minutes. Cool before serving warm.