Preheat the oven to 350°F (175°C). Grease and flour the cake pans.

In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, cinnamon, and salt.

In another bowl, mix the oil and eggs until well combined. Stir in the grated carrots and crushed pineapple.

Combine the wet ingredients with the dry ingredients and mix until just combined. Fold in the walnuts if using.

Divide the batter evenly between the prepared cake pans.

Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.

Allow the cakes to cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

In a mixing bowl, beat the cream cheese and butter together until smooth.

Gradually add the powdered sugar and vanilla extract, mixing until well combined and fluffy.

Once the cakes are completely cool, spread a layer of frosting on top of one cake layer, then place the second layer on top and frost the top and sides of the cake.