Heat the oil in a large saucepan over medium-high heat.
Season the steak with ½ teaspoon salt and ¼ teaspoon pepper and cook until browned, about 5 minutes. Transfer to a bowl and set aside.
Add the mushrooms and onions to the pan and cook until the liquid has evaporated.
Add the wine and simmer until reduced by half, 5 to 6 minutes.
Stir in the soup and ¼ cup water and bring to a boil.
Add the steak and the juices from the bowl and simmer, 2 minutes. Divide into individual bowls and sprinkle with the parsley, if using.