Coat slow-cooker bowl with nonstick cooking spray.
Add brisket, onion and garlic. In a medium bowl, combine tomatoes, ketchup, brown sugar, molasses, Worcestershire sauce, chili, mustard and cumin. Stir into beef and onions. Cover and cook on LOW for 10 hours.
Stir in beans and cook for 30 minutes. Serve with rice. Garnish with scallion and, if desired, lime wedges.