Preheat oven to 350°F. Line bottom of two 9-inch cake pans with parchment paper or use silicone pans.
Stir together the almond flour, coconut flour, baking soda, baking powder, cinnamon, nutmeg, and allspice (or ginger) in a medium bowl. Set aside.
In large mixing bow, whisk together coconut oil, eggs, and vanilla extract. Stir in zucchini, carrots, and sweetener. Then add flour mixture and stir until well combined.Stir in walnuts, if using.
Spread batter evenly between the two cake pans. Smooth tops if necessary.
Bake for 25-30 minutes until browned on top and cake is firm to the touch.
Remove from oven and allow to cool on a cooling rack before frosting.
Cream together the cream cheese and butter with an electric mixer.
Add powdered sweetener and beat until smooth.
Beat in the vanilla extract and heavy whipping cream until light and fluffy.
Sweetener can be adjusted to taste. To reduce erythritol, I often lessen the sweetener used an add in concentrated stevia to taste.Both the zucchini and carrots should be finely grated versus chunky for the best cake texture.Pecans or hazelnuts can be used instead of walnuts.If using nuts, it's best to toast them in a dry skillet on the stove. Just put the heat on medium and stir them often until they become fragrant.Spices can be changed up. Ground cloves and ginger are nice additions.