Preheat your oven to 350 degrees F.
In a 12x8 oval baking dish, arrange the peeled and sliced Granny Smith apples.
Mix together granulated sugar, cinnamon, and nutmeg. Ensure everything is well combined and toss it over the apples.
In a medium bowl, blend flour, oats, baking powder, brown sugar, butter, and salt. Cut with a fork or pastry cutter until crumbly.
Take the streusel topping and spread it in a single layer over the apples.
Bake for 30-35 minutes or until the top turns a beautiful golden brown.
Serve it up with a drizzle of salted caramel, a sprinkle of sea salt flakes, and a generous scoop of vanilla bean ice cream.