Tear off 2 1/2-foot length of 18-inch-wide foil.
Place meat in center; sprinkle with onion-soup mix; cover with vegetables.
Dot vegetables with butter and sprinkle with salt.
Fold foil over and seal securely to hold in juices.
Place on baking sheet; bake in very hot oven (450°) 1 to 1 1/2 hours or till done.