Preheat the oven to 350 degrees F (175 degrees C). Grease a 2-quart casserole dish.

Bring a large pot of lightly salted water to a boil; add zucchini. Cook at a boil until crisp-tender, about 5 minutes. Drain.

Transfer zucchini to a large bowl; stir in condensed soup, sour cream, carrots, and onion. Set aside.

Combine stuffing mix and melted butter in a bowl; spread 1/2 into the prepared casserole dish. Layer zucchini mixture over top; cover with remaining 1/2 stuffing mixture.

Bake in the preheated oven until golden brown on top, about 20 minutes.