Peel, core, and slice the apples. Mix them with the sugar, flour, and cinnamon in a bowl, then place in a large greased baking dish.
Preheat the oven to 180°C (356°F).
In another bowl, mix the oat flakes, brown sugar, and flour. Add the softened butter and chopped pecans, then mix until combined. Pour the mixture over the apples.
Bake for about 40 minutes until the topping is golden brown and the apples are tender.
Serve fresh from the oven with a scoop of vanilla or cream ice cream and homemade caramel sauce.