In a 12x8 oval baking dish add peeled and sliced granny smith apples. Toss together the, granulated sugar, cinnamon and nutmeg. Make everything is mixed well together.
In a medium bowl, mix the flour, oats, baking powder, brown sugar, cinnamon, butter and salt. Cut with a fork or pastry cutter.
Take the streusel topping and arrange it in a single layer over the apples.
Bake for 30-35 minutes or until the top is golden brown. Serve salted caramel, sea salt flakes, and a scoop of vanilla bean ice cream.