Remove excess fat from meat. Cut meat to fit into a 3 1/2- or 4-quart slow cooker. Cook meat in a large skillet in hot oil over medium heat until brown on all sides. Drain off fat. Place carrots, celery, onion, and garlic in cooker. Sprinkle tapioca over vegetables. Place meat on top of vegetables. Combine in a medium bowl undrained tomatoes, tomato paste, salt, pepper, and bay leaf. Pour over mixture in cooker.
Cover and cook on low-heat setting for 10 to 12 hours or on high-setting for 4 to 5 hours.
Remove meat to a serving platter. Skim fat from sauce. Remove and discard bay leaf. Drizzle some of the sauce overmeat. Pass remaining sauce.