Preheat oven to 350°F. Grill lamb sausage on medium-high heat for 10 to 12 minutes until cooked thoroughly (sausage is done when moisture releases from links). Let cool in refrigerator. Slice on a bias.
Place focaccia bread in a large bowl. In a nine-inch casserole pan, sauté garlic, onions, and celery over medium-high heat for three to five minutes, or until onions are translucent. Add cooked vegetables to focaccia. Next, add the sausage, Parmesan cheese, pineapple sage, chicken stock, salt, and pepper. With a spoon, stir ingredients until all are well incorporated.
Place dressing in an oven-safe baking dish, drizzle with olive oil, and bake for 20 to 25 minutes, or until the top is golden brown. Let cool for five minutes before serving.