Grease baking pans and set the oven temperature at 350ºF.
Place a sieve over a mixing bowl and pass through the flour, baking powder, baking soda, nutmeg, cinnamon and salt. Mix and set aside.
In the bowl of the mixer beat together sugar, shreded zucchini and egg. Lower the speed and slowly add in the oil and the lemon zest. Mix well
Working 1/2 cup at the time, add in the flour mixture to the bowl of the mixer, while continuing to beat at low speed, until all the flour mixture is incorporated. Gently fold in the chopped walnuts or pecans
Pour batter into baking pans, dividing equally. Bake for about 35 minutes, or until a wooden pick inserted in the center comes out “almost” clean (I like to remove from the oven when the cake is still slightly undone, because it will continue baking just outside of the oven)
Place cakes over cooling racks and let them cool down completely. Remove cakes from pans and wrap in plastic wrap if they will not be used inmediately (you can reserve them until the next day)
Make the frosting:
In the bowl of the mixer, beat the butter until soft. Add the cream cheese and beat. Lower the speed and add the icing sugar, 1/2 cup at the time, until combined
Assemble the cake:
With a serrated knife, slice off horizontally the round top of each cake to obtain two flat cakes. Place one cake on a plate, cut-side up. Spread about 3/4 cup of frosting with an offset spatula. Place the second cake on top, cut-side down. Make sure the cake is leveled. Spread the remaining frosting evenly over the top and sides of the cake, using an offset spatula and a frosting blade to evenly spread the frosting over the sides of the cake.
Decorate to your liking. I lined a few whole pecans around the top and filled it with some more chopped pecans
Refrigerate.
Notes
Note: if the frosting gets too soft while spreading it on the cake, place it in the fridge for a few minutes