1. Trim fat from the meat and thinly slice across the grain into bite size strips. Add meat to a 3 1/2 to 4 quart slow cooker and stir together with the tomato sauce, onion, water, tapioca, mustard, garlic, bouillon, and pepper. If a smoother sauce is desired, grind the tapioca in a coffee grinder or blender.
2. Cover slow cooker with the lid and cook for 7 to 9 hours on low or 3/12 to 4 1/2 hours on the high setting. Serve over hot cooked noodles or mashed potatoes.