Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with cooking spray or butter to prevent sticking.

In a large bowl, whisk together the flour, sugar, baking powder, baking soda, cinnamon, nutmeg, and salt until evenly mixed.

In another medium bowl, combine the vegetable oil and eggs. Whisk until well blended. Then, pour this mixture into the dry ingredients and stir just until combined.

Fold in the grated carrots and nuts (if using) with a spatula, ensuring they are evenly distributed throughout the batter.

Pour the mixture into the prepared baking dish and spread it evenly. Bake for 25–30 minutes, or until a toothpick inserted in the center comes out clean.

Allow the baked bars to cool in the pan on a wire rack for about 10-15 minutes, then transfer them to a wire rack to cool completely.

In a mixing bowl, blend together the softened cream cheese and butter until smooth. Gradually add the powdered sugar, vanilla extract, and a pinch of salt, whipping until creamy.

Once the bars are completely cool, spread the cream cheese frosting over the top with a spatula.

Cut the bars into squares and enjoy!