Trim any fat from roast and cut to fit cooker. Rub cajun seasoning all over meat.
Add oil to lg skillet, place over medium heat. Brown meat on all sides.
In a 4-quart slow-cooker, combine tomatoes, onion, celery, tapioca, and garlic. Place raost meat on top of veggies. Cover, cook on low for 10 hrs, or on high for 6 hrs. Slice meat and serve over hot cooked rice.