Preheat oven to 350°F (175°C). Grease two 9-inch round cake pans and line the bottoms with parchment paper circles.
In a large bowl, whisk together flour, baking soda, cinnamon, nutmeg, ginger, and salt until evenly distributed.
In a separate bowl, whisk together sugar and oil until combined. Add eggs one at a time, whisking well after each addition until the mixture is smooth and pale.
Fold the wet ingredients into the dry ingredients using a spatula until just combined with no dry streaks visible. Do not overmix.
Gently fold in the grated carrots, drained pineapple, and walnuts if using, distributing them evenly throughout the batter.
Divide batter evenly between prepared pans and smooth the tops. Bake for 28-32 minutes until a toothpick inserted in the center comes out with just a few moist crumbs.
Cool cakes in pans on a wire rack for 15 minutes, then turn out onto the rack and peel off parchment. Cool completely before frosting, at least 1 hour.
For the frosting, beat cream cheese and butter together until smooth and fluffy, about 2 minutes. Add powdered sugar one cup at a time, beating on low until incorporated, then increase speed and beat until light and creamy.
Beat in vanilla extract. Place one cake layer on a serving plate, spread with one-third of the frosting, top with second layer, and frost the top and sides with remaining frosting.
Refrigerate the frosted cake for 30 minutes to set the frosting before slicing and serving.
