Preheat oven to 350 degrees F (176 C).
Peel apples, quarter, remove cores, and use a paring knife to thinly slice lengthwise (see photo).
Add to a large mixing bowl and top with remaining filling ingredients. Toss to combine. Add to a 9x13-inch (or similar size) baking dish (adjust pan size if altering number of servings).
Rinse and wipe out your mixing bowl and add all topping ingredients. Stir to combine, then use fingers to break down any clumps of sugar. Pour over apples in an even layer.
Bake for 50 minutes to 1 hour (uncovered) or until the filling is bubbly, the apples are very fork tender (especially in the center of the dish), and the topping is deep golden brown.
Let rest at least 30 minutes before serving. This is delicious with coconut whipped cream or vanilla bean coconut ice cream.
Best when fresh, though leftovers keep covered in the refrigerator up to 3 days, or in the freezer up to 1 month. Reheat in the microwave or in a 350-degree F (176 C) oven until warmed through.