Preheat the oven to 350°F. Spray a 9-inch square baking dish, 10-inch cast iron skillet, or 11 x 7-inch dish (or other similar 2-2 ½ quart dish) with nonstick cooking spray.
In a large bowl, stir together filling ingredients. Transfer filling to prepared dish and set aside.
In a separate bowl, stir together the oats, flour, brown sugar, granulated sugar, cinnamon, and salt. Add the butter and mash with a fork (or your fingers) until you have a crumbly mixture.
Sprinkle the topping evenly over the apple filling.
Bake for about 45 minutes, or until the top is golden brown and crispy and the apples are soft. If your apples are sliced a little bit thicker, they may need 50-60 minutes in the oven to soften. Remove from the oven and let cool for at least 5-10 minutes. Serve warm or at room temperature. Top with vanilla ice cream and caramel sauce if desired.