Add grated zucchini and eggs and mix together well.
Add the dry ingredients - flour, baking powder, baking soda, salt, and cinnamon. Mix to combine.
Divide cake batter equally into the cake pans.
Bake at 350 degrees for 35 to 40 minutes or until a toothpick inserted in the center comes out clean.
Remove the cake from the pans and place them on wire racks. Cool completely before frosting.
Cream Cheese Frosting
Cool the walnuts completely.
Allow butter and cream cheese to soften at room temperature.
Using an electric mixer, beat cream cheese and butter together in a large bowl until thoroughly combined and smooth.
Slowly add in powdered sugar while mixing on low speed.
Add vanilla extract and mix it into the frosting.
Frosting the Cake
Place one cake layer on a cake plate or cake stand.
Spread frosting on top of the cake layer.
Place the second cake layer on top.
Spread frosting on the top and sides of the cake.
Lightly toast the black walnuts in the oven at 350 degrees for 8 minutes.
Chop the walnuts if they are not already chopped. Cool completely.
Sprinkle walnuts on top of the cake.
Refrigerate the cake when not serving. Keep it covered or in a cake container.You can substitute regular walnuts or pecans for black walnuts.You can use a 9 X 13-inch pan to make a single-layer zucchini sheet cake.If you want to bake the cake in a 10-inch tube or bundt pan, you will need to increase the bake time. It will take approximately 1 hour.