Place turkey breast in a 4-quart slow cooker. Add onion, olives, dried tomatoes, 1/4 cup of the broth, the lemon peel, lemon juice, garlic, salt, oregano, rosemary, thyme, and pepper.
Cover and cook on low-heat setting for 5 1/2 to 6 hours. Transfer turkey breast to a serving platter, reserving cooking juices. Cover turkey loosely with foil and keep warm.
For lemon sauce, in a medium saucepan whisk together flour and the remaining 1/4 cup broth until smooth. Stir in the reserved cooking juices. Bring to boiling over medium heat; reduce heat. Simmer, uncovered, for 8 to 10 minutes or until thickened, stirring frequently. Slice turkey breast and serve with lemon sauce.