Preheat grill to medium-high heat
In a large resealable plastic bag combine mustard, steak sauce, garlic, and parsley. Massage the bag to combine the ingredients.
Place steak into bag with the marinade and massage bag to coat steaks. Allow to marinate for a least 30 minutes or as long as overnight, refrigerated.
Remove steaks from bag and sprinkle both sides with the steak seasoning. Place on a well oiled grill and cook 4 minutes per side for medium-rare.