This is another one of those fabulous recipes from the cookbook CookThis Not That.  Followed the recipe exactly - it was perfect! 

GRILLED FLANK STEAK with Chimichurri sauce (herb sauce)

1/4 cup red wine vinegar
3 TBSP water
4 cloves garlic, minced
1 tsp salt
1 tsp pepper
1 tsp red pepper flakes
1/4 cup olive oil
1 cup finely chopped fresh parsley
1 1/2 lb flank, skirt or sirloin steak (i used skirt)

(Pull meat out of refrigerator while preparing the sauce to get the chill off and it will cook much more evenly.)

To make the chimichurri sauce, mix the vinegar, water, garlic, salt, pepper and pepper flakes.  Whisk in the oil.  When everything is blended, whisk in the parsley.

Rub steak with about a tablespoon of olive oil on each side and season with salt and pepper.  Place steak on hot grill.  For medium-rare, cook it for 3 minutes on each side.  Take steak off grill let sit for 3 minutes before slicing.  Slice diagonally against the grain to make it tender.  Drizzle with sauce.

(I keep thinking I need to take a picture of these recipes so you can see, but I always think of it after my hungry family has devoured it.)