In 4-quart Dutch oven, heat oil over medium-high heat. Place chicken, skin sides down, in hot oil; add onion and garlic. Cook 6 to 10 minutes, turning chicken occasionally, until chicken is brown on all sides.
Reduce heat to medium. Sprinkle cilantro, cumin, turmeric, ginger and salt over chicken. Add cinnamon stick; pour broth and tomatoes over chicken. Turn chicken several times to coat evenly. Add plums, olives and lemon, pressing into liquid around chicken. Reduce heat to low. Cover and simmer about 30 minutes or until juice of chicken is clear when thickest part is cut to bone (170°F for breasts; 180°F for thighs and legs).
Remove chicken to deep serving platter; cover to keep warm. Increase heat to high; boil sauce uncovered about 5 minutes, stirring occasionally, until thickened. Pour sauce over chicken. Garnish with additional chopped fresh cilantro if desired. Serve over couscous.