Pat steaks dry. Sprinkle with salt and pepper, then rub with half the olive oil.
Heat a heavy skillet and brush with remaining olive oil. Add steaks and cook to medium rare—5 to 6 minutes per side if steaks are 1½ inches (4 cm) thick, or until a meat thermometer registers 130°F (55°C). Remove steaks from pan. Return pan to heat.
There should be a little oil left in the pan; if not, add about 1 tsp (5 mL). Add shallots and cook for about one minute. Add vinegar. Cook, stirring, until vinegar evaporates and shallots begin to brown. Add mushrooms and cook for 2 minutes. Add wine. Cook on medium-high heat, stirring, until about half the wine has evaporated. Add oyster sauce and cook the mixture for a few minutes, until mush-rooms are glazed and there are a few tablespoons of sauce in the pan.
To serve, top the steaks with mush-rooms and shallots. Sprinkle with parsley.