Preheat oven to 350 degrees. Remove excess fat from shanks. Wipe with damp paper towels. Coat well with flour. Slowly heat oil in Dutch oven. In it, brown shanks well, turning on all sides.
Add garlic, salt, oregano, pepper, broth and lemon juice; cover. Bake 1 1/4 to 1 1/2 hours or until lamb is almost tender. Turn shanks; add carrots, onions, celery and potatoes; cover. Bake 35 to 45 minutes or until meat and vegetables are tender.
Remove shanks to serving platter; surround with vegetables; cover and keep warm. Measure liquid in casserole (about 1 1/2 cups). Skim off excess fat, reserving 1 tablespoon in medium saucepan. Blend 1 tablespoon flour into fat. Gradually stir in skimmed liquid. Bring to boil, stirring. Boil 1 minute, pour over shanks and vegetables.