Preheat your oven to 375°F (190°C) or prepare your campfire to medium-high heat.
In a medium bowl, toss the sliced apples with 1/2 cup of the brown sugar and 1/2 teaspoon of cinnamon.
In a separate bowl, combine the oats, flour, remaining brown sugar, salt, and melted butter to form the crumble topping.
Lay out four large squares of aluminum foil.
Divide the apple mixture evenly into the center of each foil sheet.
Top each portion of apples with a generous scoop of the oat crumble mixture.
Fold the foil edges over the top to create a sealed packet, leaving a little room for steam to circulate.
Place the packets on an oven tray or directly on the campfire grate.
Cook for 20-25 minutes until the apples are tender.
Carefully open the packets, drizzle with caramel sauce, and serve warm.