Preheat the oven to 350 degrees F (175 degrees C).
Bring a large pot of water to a boil. Cook zucchini and onion in boiling water for 5 minutes; drain well.
Combine condensed soup, sour cream, and carrots in a large bowl; stir in zucchini and onion until well combined. Set aside.
Combine stuffing mix and melted butter in a bowl; spread ½ into a 9x13 inch baking dish. Spoon zucchini mixture over stuffing; top with remaining ½ stuffing mixture.
Bake in the preheated oven until stuffing is golden brown, 25 to 30 minutes.
Summer Zucchini Casserole · Dinner Match Lab | Dinner Match Lab