To prepare steak, sprinkle salt and pepper evenly over both sides of steak. Place steak on a broiler pan coated with cooking spray; broil 5 minutes on each side or until desired degree of doneness. Remove the steak from oven; loosely cover with foil.
To prepare sauce, heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add 1/2 cup onion and garlic; sauté 2 minutes. Add mushrooms; sauté for 4 minutes. Add broth, wine, and vinegar. Bring to a boil; reduce heat to medium, and cook until reduced to 1 1/4 cups (about 6 minutes). Add green onions, and cook for 1 minute.
Slice steak diagonally across the grain into 1/4-inch slices. Serve steak with mushroom sauce.
My husband and I found this to be terribly bland. The sauce was okay but very vinegar-y. The steak needed MUCH more seasoning than just salt & pepper. I saved the steak to make fajitas or quesadillas with it but tossed the sauce. FYI: I followed the recipe to a T.
The dish is easy to make and the sauce is very good. Flank isn't my favorite cut but it makes for a nice, everyday meal. I think I'm going to try the sauce on some tenderloins which could turn this into a dish worthy of company.
I am really confused by all of these stellar reviews. I made this recipe for my husband's birthday - what a HUGE disappointment! The meat was flavorless (I grillled it) as was the sauce. One of you suggested "marinating it longer", I don't see anything in the directions saying to marinate it at all! I followed the recipe exactly. Luckily my guests had tasted other fine recipes from Cooking Light, this one will not be returning to my table.