Cook sliced squash or zucchini & chopped onion in salted water, boiling 5 minutes, drain. combine the soup & sour cream. Stir in shredded carrots. Fold in drained squash & onion. Combine stuffing mix & butter. Spread 1/2 of stuffing mixture in bottom of 11x8x2 inch baking dish. Spoon vegetable mixture over top with remaining stuffing. Bake at 350 for 25-30 minutes or till heated thoroughly.