Boil squash and onion till tender. Reserve 1 1/2 cups of juice from squash. Stir fry ground round till pink is gone and crumbly.
Line 8x13 casserole dish with 1/2 of stuffing mix. Layer squash and ground round. Top with 1/2 of cheese and 1/2 of margarine. Then top with the rest of stuffing and cheese and margarine. Top all of casserole with the liquid that has been reserved.