Preheat oven to 350°F (175°C) and line two large baking sheets with parchment paper.

In a medium mixing bowl, whisk together the all-purpose flour, ground cinnamon, baking soda, and salt until homogenous.

In a separate large bowl, cream the softened butter with brown sugar and granulated sugar using an electric mixer until the texture is light and aerated.

Add the egg and vanilla extract to the butter mixture, beating on medium speed until fully emulsified.

Reduce mixer speed to low and gradually add the dry flour mixture until just combined; do not overmix.

Using a rubber spatula, fold in the rolled oats, finely grated carrots, and chopped walnuts until evenly distributed.

Scoop rounded tablespoons (approximately 28g each) of dough onto the prepared baking sheets, spacing them 2 inches apart to allow for lateral expansion.

Bake for 10 to 12 minutes or until the edges are set and lightly browned while the centers remain slightly soft.

Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes to set the structure before transferring to a wire cooling rack.