Preheat the oven to 425°F (220°C).
In a large mixing bowl, combine the sliced apples, granulated sugar, cinnamon, nutmeg, lemon juice, and flour. Toss until the apples are well coated.
Pour the apple mixture into the pre-made pie crust, spreading it evenly.
Drizzle the caramel sauce over the apples, ensuring even coverage.
In another bowl, mix the rolled oats, brown sugar, melted butter, vanilla extract, and salt until crumbly.
Sprinkle the oat mixture over the caramel apple filling in the pie.
Bake in the preheated oven for 15 minutes. Reduce the temperature to 350°F (175°C) and continue baking for an additional 30-35 minutes, or until the apples are tender and the topping is golden brown.
Remove from the oven and let cool for at least 15 minutes before serving.