1. Preheat the oven to 350 degrees F (175 degrees C).
2. Grease 2 (8-inch) cake pans and line with parchment paper, then grease the parchment paper.
3. In a mixing bowl or a stand mixer fitted with the paddle attachment, combine brown sugar, apple sauce, canola oil, eggs, vanilla, cinnamon, baking soda, and salt. Mix on medium speed until well blended.
4. Add the flour and mix until fully incorporated.
5. Fold in the grated carrots, grated zucchini, walnuts (if using), and drained pineapple. Mix thoroughly.
6. Divide the batter evenly between the two prepared pans and bake for 55 minutes or until a toothpick inserted in the center comes out clean.
7. Allow the cakes to rest in the pans for 5 minutes, then remove from the pans and transfer to a cooling rack. Cool until room temperature.

Cream Cheese Frosting

1. In the stand mixer, cream together the softened butter and cream cheese until well combined.
2. Add vanilla extract and mix until incorporated.
3. Gradually add sifted powdered sugar until your desired consistency is achieved.
4. Chill the frosting in the refrigerator for 30 minutes to an hour for improved handling. This recipe yields a softer, less sweet frosting with 3 cups of powdered sugar, but you can adjust according to your taste preference.
5. Frost the cooled cake and refrigerate until ready to serve.