Cook squash and onion in boiling salted water for 5 minutes in a pan. Combine soup, carrots, chicken, sour cream, and cheese. Fold in drained squash and onion. In a separate bowl, combine stuffing mix and butter. Spread 1/2 stuffing mix in large casserole dish. Spread vegetable mix on top. Sprinkle remaining stuffing mixture over the top.

Bake at 350°F for 25-30 minutes.