Mix Chimichurri Blend, water, olive oil and red wine vinegar in large bowl. Transfer 1/3 of mixture to small bowl and set aside. Add flank steak to the large bowl and toss to coat the mixture on both sides. Cover bowl, and place in refrigerator for at least 1 hour, and up to 4.
Heat grill over medium-high heat. Remove steak from marinade, and place on grill. Cook for 4 to 5 minutes, or until browned on bottom. Flip, and brown on the other side, 4 to 5 minutes, or until meat thermometer registers internal temperature of 130°F.
Remove flank steak and let rest for at least 5 minutes.
Thinly slice steak against the grain. Serve with reserved Chimichurri sauce.
