3 large Granny Smith apples, peeled, cored, and sliced  
¼ cup apple cider
1 tablespoon freshly squeezed lemon juice
2 tablespoons cornstarch
1 teaspoon ground cinnamon
Pinch of nutmeg

Topping
½ cup rolled oats, certified gluten-free
½ cup walnuts, finely chopped (optional)
½ cup light brown sugar
1 teaspoon ground cinnamon
2 tablespoons softened unsalted butter

Preheat oven to 350 degrees F. Spray an 8x8 baking dish with nonstick cooking spray.
In a large bowl, toss together sliced apples, lemon juice, apple cider, cornstarch, cinnamon, and nutmeg. Transfer to the baking dish.
In a separate bowl, combine all of the topping ingredients together by mixing with your hands. Make sure that the butter is well dispersed throughout.
Sprinkle the topping mixture evenly over the apples. Bake for 25-30 minutes, until apples are soft, juices are bubbling, and the topping is browned.
Serve immediately.