Preheat oven to 350°.
Toss apples, ¼ cup of brown sugar and 2 tablespoons melted butter in a greased 2-quart baking dish.
Toss oats, whole wheat flour, cinnamon, salt, remaining brown sugar and melted butter in a small bowl until evenly mixed (mixture will be fairly wet).
Sprinkle oat mixture over apples and bake for 50¬60 minutes, until topping is golden brown and filling is juicy and bubbly.
Let cool 10 minutes and serve topped with vanilla ice cream and drizzled with maple syrup.