Drain vegetables, reserving 3/4 cup total liquid.
In large saucepan, combine vegetables, the reserved liquid, the meatballs in gravy and the tomato sauce.
Bring to boiling.
Stir together biscuit mix and milk; drop from tablespoon in 4 to 6 dumplings onto boiling stew.
Cook, covered, for 15 to 20 minutes.