Heat oil in a Dutch oven over medium heat. Add celery, onion, and garlic. Sauté 3 minutes. Add corn, pepper, and salt. Sauté 1 minute. Lightly spoon flour into a dry measuring cup; level with a knife. Add flour to pan; cook 1 minute, stirring constantly. Stir in chicken broth and thyme; bring to a boil. Cover, reduce heat, and simmer 20 minutes, stirring occasionally.
. Add turkey, milk, and lemon juice to pan, stirring well. Cook 3 minutes or until thoroughly heated. Remove from heat, and stir in sour cream. Sprinkle with parsley, if desired.