Brush flank steak on both sides with soy sauce. Sprinkle well with salt, pepper and thyme. (Go easy on the salt because the soy sauce is salty.) Let stand for 1 hour or more. Brush again with the soy sauce and grill over a brisk fire 4 minutes on each side for rare.
Meanwhile, melt 1 tablespoon butter in small saucepan. Add shallots or green onions and sauté just until tender, about 5 minutes. Sprinkle with the thyme. Add the wine and bring just to a boil. Add the stick of butter, salt and pepper and stir until the butter is melted. Add the chopped parsley.
To serve, carve the steak in thin slices across the grain. Spoon the sauce over the sliced steaks.
Notes: It is critical to remember that with flank steak, as well as most any meat, it is essential to slice across the grain. If you slice with the grain, the meat will be tough. Also, any grilled or roasted meat requires a "resting" time after cooking to ensure that the juices will not be released. A flank steak should rest approximately 7 minutes before slicing.