Preheat your oven to 350°F or 175°C. Line baking trays with parchment paper so the cookies bake evenly and do not stick.

In a large bowl, combine flour, baking soda, baking powder, cinnamon, nutmeg, and salt. Stir everything well until evenly mixed.

Beat softened butter, brown sugar, and white sugar until the mixture becomes light, fluffy, and smooth.

Mix in the egg and vanilla extract. Beat until fully combined and the mixture looks creamy and soft.

Fold in grated carrots, rolled oats, and chopped walnuts if using. Stir gently to keep the mixture light.

Slowly add the dry ingredients into the wet mixture. Mix until a soft cookie dough forms without overmixing.

Use a cookie scoop or spoon to place equal portions onto the prepared baking sheet. Leave space between each cookie.

Bake for 10 to 12 minutes until the edges are lightly golden while the centers stay soft.

Let the cookies rest on the baking tray for five minutes. Transfer them to a cooling rack until fully cooled.

Beat cream cheese and butter until smooth. Add powdered sugar and vanilla extract. Mix until fluffy and creamy.

Spread or pipe cream cheese frosting onto each cooled cookie. Sprinkle with chopped walnuts or cinnamon if desired.