Follow these simple steps to create your Carrot Cake Bars with Cream Cheese Frosting:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and line a 9×13-inch baking pan with parchment paper.
2. Mix the Dry Ingredients: In a large bowl, whisk together the flour, granulated sugar, baking soda, baking powder, cinnamon, nutmeg, and salt.
3. Combine Wet Ingredients: In another bowl, whisk together the vegetable oil and eggs until fully combined.
4. Add Carrots and Pineapple: Stir in the grated carrots and crushed pineapple until well mixed.
5. Combine Mixtures: Gradually add the wet ingredients to the dry ingredients, mixing just until combined. Avoid overmixing.
6. Add Nuts: If using, fold in the chopped walnuts or pecans to the batter.
7. Bake: Pour the batter into the prepared baking pan and bake for 30-35 minutes. The bars are done when a toothpick inserted in the center comes out clean.
8. Cool: Allow the bars to cool in the pan for about 15 minutes, then remove them from the pan and cool completely on a wire rack.

For the Cream Cheese Frosting

9. Make the Frosting: In a mixing bowl, beat the softened cream cheese and butter until smooth. Gradually add the powdered sugar and vanilla extract. Mix until well combined. If the frosting is too thick, add a little milk to reach the desired consistency.
10. Frost the Bars: Once the carrot cake bars have cooled completely, spread the cream cheese frosting evenly over the top. Optionally, sprinkle with additional chopped walnuts or coconut.