Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a large mixing bowl, whisk together the rolled oats, all-purpose flour, brown sugar, granulated sugar, baking soda, ground cinnamon, nutmeg, and salt.

In another bowl, cream together the unsalted butter and sugars until light and fluffy, then mix in the egg and diced apples.

Slowly add the wet mixture to the dry ingredients, stirring gently until just combined.

Drop rounded balls of dough onto the prepared baking sheet, leaving about 2 inches between each cookie.

Bake for 10-12 minutes, or until golden around the edges and just set in the center.

Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack.