Preheat oven to 200 degrees C. In a bowl combine the sausage meat, mushrooms, onion, garlic, butter, herbs to taste, salt and pepper and 2 tablespoons olive oil. Stuff turkey with the mixture. Brush the turkey with the remaining 2 tablespoons oil and sprinkle with some more herbs.
Place the turkey on a rack in a roasting tin. Roast 2 1/2 hours, covering with foil as soon as it browns a bit. Remove the foil for the last 30 minutes of roasting.