Preheat oven to 375°F.
On 18 x18-inch piece heavy-duty aluminum foil, place steak; sprinkle both sides of steak with onion soup mix.
Wrap foil loosely around steak, sealing edges airtight with double fold.
Place in 13x9-inch baking or roasting pan and bake 1 hour or until steak is tender.
Thicken gravy, if desired, and pour over steak.