Heat the oil in a small skillet over medium to medium-high heat. Once hot, add the mushrooms and cook until softened and starting to brown, about 4 to 5 minutes, stirring frequently.
Turn the heat down to low, add the garlic, and cook 1 minute, stirring constantly.
Add the water use a wooden spoon to scrape up any brown bits that have formed on the bottom of the skillet.
Stir in the cream cheese, Worcestershire sauce, and black pepper, and cook until heated throughout, about 3 minutes, stirring constantly.
To serve, reheat the steak on a hot grill or skillet. Transfer the steak to a plate, top with the mushroom sauce, and sprinkle on the parsley.