How to Make It
In a food processor, combine the cilantro with the red onion, serrano chile, garlic, lime juice, 1 tablespoon of olive oil, Worcestershire sauce, mustard and a generous pinch each of salt and pepper. Puree until nearly smooth. Scrape the marinade into a large resealable plastic bag. Add the steak pieces and turn until well coated. Seal the bag and refrigerate for at least 3 hours or overnight.
Remove the steak from the marinade and let stand at room temperature for 15 minutes.
Light a grill or preheat a grill pan. Brush the steak with oil and season with salt and pepper. Oil the grill grates and grill the steak over high heat, turning once or twice, until lightly charred outside and medium-rare within, 5 to 6 minutes. Transfer the steak to a carving board, let rest for 5 minutes and slice across the grain; serve with the tortillas, garnishes, Pecan-Chipotle Salsa and limes.