Combine all marinade ingredients in a 13' x 9' inch glass baking dish.
Add the flank steak. cover with plastic wrap and marinate for at least 2 hours (no more than 4) in the refrigerator. Make sure both sides are marinated by turning the steak over once during marinating time.
Remove steak from marinade, letting excess marinade drip off. Sprinkle lightly with salt and generously with pepper on each side. Rest the meat for 10 minutes to get rid of refrigerator chill.
Use your favorite grilling method, and cook on each side for 4-6 minutes (for medium rare).
Remove from grill, sprinkle with feta, cover with foil, and let rest 5-7 minutes.
Remove foil, cut the steak in thin slices against the grain and on a diagonal, and serve with sliced tomatoes, cucumbers, and extra feta if desired. I serve with toasted and oiled baguette slices as well.