Pour 1/2 cup of the chimichurri into a large resealable plastic bag. Add the skirt steaks and marinate overnight in the refrigerator. (Reserve the rest of the chimichurri for serving). Prepare a hot fire in a grill. (Prepare the onions while the grill heats.) Remove the steaks from the marinade and, turning once, grill to desired doneness. (Because they are thin and have been marinating overnight, they will cook very fast.) Cut each steak in two, arrange them in the center of four warm plates, and season with salt and pepper. Top with the onions and garnish with the olives and parsley. Serve with the reserved chimichurri on the side. Recommended wine: A Nebbiolo d`Alba or a Cabernet Sauvignon from Mendoza, Argentina.