In 4-quart Dutch oven, heat oil over medium-high heat. Cook onion in oil 2 minutes, stirring occasionally. Add carrots and celery; cook 2 minutes longer, stirring occasionally. Stir in all remaining ingredients except turkey and spinach.
Heat to boiling; reduce heat. Cover and simmer 15 to 20 minutes, stirring occasionally, until lentils are tender. Stir in turkey and spinach; simmer 2 to 3 minutes longer or until turkey is hot.