Preheat oven to 325°F. Heat the butter in a large sauté pan. Sauté the onion and garlic for about 5 minutes over medium heat. Add celery and scallions and sauté for 2 more minutes. In a large bowl, mix the onion mixture with all the remaining ingredients. Place the stuffing in a well-greased baking dish. Bake for 1 hour.