Place turkey breast, onion, kalamata olives, sun-dried tomatoes, ¼ cup chicken broth, lemon juice, Greek seasoning, salt, and pepper in the crock of a slow cooker.
Cover and cook on Low for 7 hours.
Combine remaining ¼ cup chicken broth and flour in a small bowl; whisk until smooth. Stir into the slow cooker.
Cover and cook on Low for 30 more minutes.
