In a large bowl, combine the sliced apples, brown sugar, and cinnamon.
In a separate bowl, combine the gluten-free flour, rolled oats, brown sugar, and cold butter. Use a pastry blender or your fingers to cut the butter into the dry ingredients until the mixture resembles coarse crumbs.
Pour the apple mixture into a baking dish. Sprinkle the crumble topping evenly over the apples.
Bake for 35-40 minutes, or until the topping is golden brown and the apples are tender.
Notes
Serve warm with a scoop of vanilla ice cream or whipped cream.