Heat the oil in a large heavy-bottomed soup pot. Lightly sauté the onion, celery, and bacon. Add the pumpkin, water, apple cider, brown sugar, five-spice, bouillon, apple, liquid smoke, salt, pepper, and ginger root to the pot. Cover and simmer for 35–40 minutes, stirring frequently. Pureé in a blender or food processor in batches until smooth. Serve with a dollop of sour cream, if you wish.