Pour 1/2 cup Marie’s Balsamic Vinaigrette over steaks and onion slices. Marinate while cooking mushrooms.
Heat olive oil in pan. Sauté mushrooms for about 7 minutes, stirring occasionally, or until liquid from mushrooms has evaporated. Stir in remaining 1/4 cup Marie’s Balsamic Vinaigrette; remove from heat.
Grill steaks and onion slices. Place each steak on serving plate; top with onion separated into rings. Spoon mushrooms over steak, sprinkle with cracked black pepper and top with crumbled blue cheese.