Preheat oven to 350 degrees F. Lightly grease the bottoms and 1/2 inch up the sides of four 5 3/4x3x2-inch loaf pans; set aside.
In a large bowl, stir together cake mix, eggs, the water, oil, vanilla, cinnamon, and nutmeg until smooth. Stir in zucchini, carrot, and 1/4 cup pecans. Divide batter among the prepared loaf pans, spreading evenly.
Bake in the preheated oven about 35 minutes or until a toothpick inserted near centers comes out clean. Cool in pans on wire racks for 5 minutes. Remove from pans; cool completely on racks. Wrap and store overnight before slicing.
Drizzle Cream Cheese Icing over loaves before serving. If desired, sprinkle with additional pecans.
Cream Cheese Icing
In a small bowl, stir together cream cheese, butter, and vanilla. Stir in powdered sugar and enough milk to make an icing of drizzling consistency.