Sprinkle steaks evenly with 1 tsp. salt, pepper, and garlic powder. Place steaks on a lightly greased rack in an aluminum foil-lined broiler pan.
Broil steaks 7 to 8 inches from heat 6 to 7 minutes on each side or to desired doneness. Remove steaks from oven.
Melt butter in a small saucepan over medium-high heat; add mushrooms. Sauté mushrooms 3 minutes or until lightly browned; add remaining 1/8 tsp. salt. Arrange steaks on a serving platter, and top evenly with mushrooms. Sprinkle with chopped parsley.