Cook sausage until well cooked and no longer pink over medium-high heat, turning regularly in a sizable saucepan or stockpot. Add the mushrooms, onion, carrots, celery, and garlic; stir constantly for 10 to 12 minutes, or until the onion is transparent. Add remaining ingredients and stir thoroughly after transferring mixture to a large bowl. Pour into a 4-quart greased casserole.