Preheat the oven: Preheat the oven to 350°F (175°C) and grease/flour a 9×13-inch pan.
Mix dry ingredients: In a bowl, whisk flour, sugar, cinnamon, nutmeg, baking powder, baking soda, and salt.
Combine wet ingredients: Beat eggs, oil, and vanilla; mix into dry ingredients. Add zucchini and nuts, if using.
Bake: Pour batter into pan and bake for 35-40 minutes until a toothpick comes out clean.
Make frosting: Beat cream cheese and butter, add sugar, vanilla, and salt until fluffy.
Frost the cake: Spread frosting over cooled cake before slicing and serving.