Sprinkle chicken thighs evenly with salt and ½ teaspoon pepper.
Heat 1 tablespoon oil in a large skillet over medium-high heat; add half of the chicken. Cook about 3 minutes per side, or until browned. Transfer to a slow cooker. Add remaining 1 tablespoon olive oil to skillet, and repeat the procedure with remaining chicken.
Combine broth, juice, flour, and cumin, stirring with a whisk. Pour broth mixture over chicken.
Top with olives and remaining ¼ teaspoon pepper. Cover and cook on low heat for 6 hours. Add lemon slices as a garnish to serve, if using.