PLACE meat in slow cooker container; top with onions, mushrooms and tomatoes. Combine Italian seasoning and barbecue sauce. Pour over vegetables.

COOK 5 hours on HIGH (or 8 to 10 hours on LOW). Remove meat from slow cooker; shred with fork. (Or, cut across the grain into thin strips.) Return meat to slow cooker; stir gently to evenly coat with sauce.

PLACE 1 bun half on each serving plate; top with 1/4 of the meat mixture.