Stir 1 cup of the stuffing and butter in a small bowl. Set aside.
Stir soup, sour cream, zucchini, carrots and onion in a large bowl., Add the remaining stuffing and stir lightly to coat. Spoon the mixture into a 1 1/2 quart baking dish. Sprinkle with the reserved stuffing mixture.
Bake at 350 degrees F for 35 minutes or until it's hot.