Heat the oven to 400 degrees F. Place the squash, onions and garlic into a large bowl. Add the cumin and oil and toss to coat. Spoon the squash mixture onto 2 rimmed baking sheets.
Roast for 30 minutes or until the squash mixture is lightly browned, stirring occasionally.
Reduce the oven temperature to 350 degrees F. Stir the squash mixture, cilantro, celery and broth in a large bowl. Add the stuffing and mix lightly. Stir in the sausage, if desired. Spoon the stuffing mixture into a greased 3 1/2-quart casserole. Cover the casserole.
Bake for 30 minutes or until the stuffing mixture is hot.