Gather the ingredients. Preheat the oven to 350 degrees F (175 degrees C). Line a 9x13-inch baking pan with parchment.

To make the crust: Combine 2 cups flour, quick cooking oats, brown sugar, baking soda, and salt in a large bowl; stir in melted butter and mix until crumbly. Press 2/3 of crust mixture into the prepared baking pan. Bake in the preheated oven for 18 minutes.

Meanwhile, make the caramel filling: Combine caramel topping and remaining 1/2 cup of flour in a small pan over medium heat. Bring to a boil, stirring constantly, and cook for 3 to 5 minutes.

Spread apple slices evenly over baked crust; sprinkle nuts on top. Pour caramel filling over apple layer; crumble remaining crust mixture over the top of everything.

Bake in the preheated oven until top is crisp and golden brown, about 30 minutes. Cool completely before slicing into bars.