Preheat the oven to 375°F. Use a cheese grater with large shredding holes (or a food processor set to 'shred') to shred the zucchini, carrots, and apples.
In a stand mixer, combine the melted butter, orange juice, sugar, eggs, baking soda, baking powder, and spices. Slowly add the shredded zucchini, carrots, and apples until a smooth batter forms.
Add the flour 1/2 cup at a time, with the mixer set on a medium-low speed. Continue adding the flour until a thick, sticky batter forms.
Grease 3 bread pans with butter and flour. Pour the batter into each pan so they are about 2/3 full. Bake for 35-45 minutes, or until a toothpick inserted into the center comes out clean.
While the bread cools (it's best to cool completely before cutting), use a hand mixer to beat together the cream cheese, butter, vanilla, and powdered sugar until a smooth icing forms. Pour the icing evenly over the tops of each loaf and let set. Enjoy!