Preheat oven to 425 degrees F.
Combine cilantro, mustard, mustard seeds and garlic in a small bowl.
Season lamb with salt and pepper. Brush oil evenly over a small cast-iron or other ovenproof skillet. Heat skillet over medium-high heat. Add lamb, meat-side down, and cook until browned, 2 to 3 minutes. Remove from the heat and spread mustard mixture over browned side. Transfer skillet to oven and roast lamb for 15 to 20 minutes, or until an instant-read thermometer registers 140 degrees F (rare) or until lamb reaches desired doneness.
Transfer lamb to a cutting board and let rest for 5 minutes. Carve rack between the ribs. Spoon some New Mexico Chile Sauce onto 2 plates and top with lamb. Serve immediately.