Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, combine the rolled oats, all-purpose flour, baking soda, ground cinnamon, ground nutmeg, and salt. Set aside.
In a large bowl, cream together the softened unsalted butter, brown sugar, and granulated sugar until light and fluffy, about 2-3 minutes. Beat in the egg and vanilla extract until well combined.
Gradually add the dry ingredient mixture to the wet ingredients, mixing until just combined. Fold in the grated carrots, raisins, and any optional ingredients.
Scoop tablespoon-sized portions of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake for 10-12 minutes until the edges are lightly golden. Let cool on the baking sheet for 5 minutes before transferring to a wire rack.