Heat oil in a Dutch oven over medium heat. Add a single layer of mushrooms and cook, without stirring, for about 5 minutes or until mushrooms become red-brown on one side. Add onions, garlic, and celery and sauté until translucent, about 5 more minutes. Add turkey stock (see recipe below) or chicken broth, turkey, and sage. Cover and simmer over medium-low heat for 20 minutes. Add rinsed beans, spinach, lemon juice, salt, and pepper. Bring to a boil to wilt spinach and serve hot. Serves 8.
To make turkey stock: Place turkey bones in a large stockpot and cover with cold water. Add 1 quartered onion, 2 coarsely chopped stalks of celery, 1 coarsely chopped carrot, 1 bay leaf, and 2 sage leaves. Bring to a boil, reduce heat to a low simmer, and cook 2 or more hours. Strain and skim fat from top and store stock for future use.