Preheat your oven to 350°F (175°C). Line a 9×13 inch baking pan with parchment paper, leaving a slight overhang on the sides for easy removal later. Lightly grease any exposed pan surfaces with cooking spray.
In a large mixing bowl, combine the flour, oats, brown sugar, baking soda, and salt. Pour in the melted butter and stir until the mixture is crumbly and well combined. Reserve 1 1/2 cups of this mixture for the topping and set it aside.
Press the remaining oat mixture firmly into the bottom of your prepared baking pan. Bake for 12 to 15 minutes, or until the edges are very lightly browned. Remove the pan from the oven but keep the oven on.
While the crust is baking, toss the diced apples with lemon juice and cinnamon in a medium bowl. This keeps the apples from browning and adds a wonderful spiced flavor to the filling.
In a microwave-safe bowl, combine the caramel bits and heavy cream. Microwave in 30-second intervals, stirring in between, until the mixture is completely smooth and melted. Be careful not to burn the caramel.
Spread the prepared apples evenly over the pre-baked crust. Pour the melted caramel mixture over the apples, covering them as much as possible. Finally, sprinkle the reserved oat mixture over the top of the caramel layer.
Place the pan back in the oven and bake for another 20 to 25 minutes. The top should be golden brown and the caramel should be bubbling slightly. Remove from the oven and let the bars cool completely in the pan before cutting.