In a small bowl, add the parsley, lemon, salt and 3/4 of the oil. Stir to combine and set aside.
Add the remaining oil to a skillet and place the chicken on a cold skillet. Turn the heat up to medium, allowing it to cook slowly for about 4 minutes. Continue cooking over medium heat for about 8 to 12 minutes, depending on the thickness of the tuna steak. Turn the tuna over and cook for one minute more.