Place cilantro, parsley, capers, garlic, lemon juice, red wine vinegar, olive oil and black pepper in a food processor and pulse to finely chop. Let stand 20 minutes before using. Season to taste with salt before serving.
Heat grill to medium-high heat. Season the steak with salt and pepper. Brush grill with oil. Grill the steaks, turning once or twice, until desired doneness, about 7–10 minutes total for medium rare. Remove from the grill and let meat rest 5 minutes.
To serve, spoon cilantro sauce over the steak, and thinly slice the meat across the grain on a slight diagonal.
Recipe courtesy of JoAnn Hecht, owner of A Seasonal Table Catering in Simi Valley (ASeasonalTable.com).