Preheat your oven to 350°F (175°C) and lightly grease a 9×13 inch baking dish with butter or cooking spray.
Prepare the apple filling by melting butter in a large saucepan over medium heat. Add the diced apples and cook for 3-4 minutes until they begin to soften.
Stir in brown sugar, cinnamon, vanilla, nutmeg, and salt to the apples. Simmer for 2-3 minutes until the sugar dissolves and creates a syrupy texture.
Add the cornstarch slurry to the apple mixture, stirring constantly until the sauce thickens, about 1-2 minutes. Remove from heat and let cool slightly.
Open the cinnamon roll packages and set aside the icing packets for later use. Cut each cinnamon roll into quarters.
Arrange half of the cinnamon roll pieces in a single layer in the prepared baking dish.
Spread two-thirds of the apple mixture evenly over the cinnamon roll layer.
Top with remaining cinnamon roll pieces and then the remaining apple mixture. If using nuts, sprinkle them over the top.
Cover the dish with aluminum foil and bake for 20 minutes. Then remove the foil and bake for an additional 10 minutes until the rolls are golden brown and fully cooked.
Warm the reserved icing by placing the packets in a bowl of warm water for 1 minute. Drizzle over the still-warm bake and serve immediately.