To Roast the Squash:

1. Heat oven to 375°F and grease a roasting pan. Cut a thin slice off of the round side of each squash half to create a stable base. Place the squash halves cut side up on an oiled baking dish.
2. Combine the melted butter and maple syrup, and brush on the flesh side of each squash half. Season with a pinch of salt and pepper.
3. Roast for 30 minutes. Remove from oven and set aside to cool until stuffing is ready.

To make the Stuffing:

1. While squash is roasting, prepare barley. Combine barley and chicken stock in a saucepan, and bring to a boil. Turn down to a simmer, cover with a lid, and cook until liquid is absorbed and barley is tender (about 30-45 minutes). Drain and set aside.
2. When barley is almost done, prepare the rest of the filling. Heat oil in a large skillet over medium-high heat. Add sausage, celery, and mushrooms and cook while breaking up into small pieces with a spatula. When sausage is cooked through, and vegetables are tender, add garlic, thyme, and poultry seasoning, and cook for 1 more minute. Stir in cooked barley, then remove from heat. Adjust seasonings to taste.

To Assemble and Bake Stuffed Squash:

1. Divide the stuffing mixture between the squash halves, spooning the stuffing into the hollow center of each squash. Sprinkle with grated Parmesan, and return to oven to bake for 15 minutes.
2. Remove from oven, and allow to cook for 5 minutes before serving.