Heat a large Dutch oven coated with cooking spray over medium-high heat. Add 2 lamb shanks; cook 10 minutes, browning on all sides. Remove from pan. Repeat procedure with remaining lamb; remove from pan.
Add onion and garlic to pan; sauté 2 minutes. Add dry Marsala; cook 2 minutes, stirring frequently. Add broth, tomato sauce, rosemary, salt, pepper, and cinnamon stick.
Return lamb to pan; bring mixture to a simmer. Cover pan and bake at 350° for 1 hour.
Remove lamb mixture from oven; stir in raisins. Cover and bake an additional 45 minutes or until lamb is tender. Remove cinnamon stick; discard. Serve lamb with pan sauce and Cucumber Raita. Garnish with mint sprigs, if desired.