Preheat the oven to 350°F (175°C).
In a large bowl, whisk together flour, oats, baking soda, cinnamon, and salt.
In another bowl, cream together softened butter, brown sugar, and granulated sugar until light and fluffy.
Add the egg to the butter mixture and mix until combined.
Gradually mix the dry ingredients into the wet mixture until just combined.
Fold in the diced apples, caramel sauce, and walnuts if using.
Drop rounded tablespoons of dough onto a baking sheet lined with parchment paper, leaving space between each cookie.
Bake for 12-15 minutes, or until the edges are golden brown.
Remove from the oven and let the cookies cool on the baking sheet for a few minutes before transferring to a wire rack.