1To prepare the marinade, rehydrate the dried guajillo chiles by placing them in a small pot, covering with hot water, and simmering for 10 minutes until softened. Drain and set aside.
2In a blender, combine the rehydrated dried guajillo chiles, juice from the Limes (150g), juice from the Oranges, 10g of Garlic cloves, 50g of White onion, 10g of Cilantro, Cumin powder, Mexican oregano, 10g of Sea salt, and Black pepper. Blend until very smooth.
3Place the Skirt steak in a shallow dish or a large resealable bag. Pour the marinade over the Skirt steak, ensuring it is fully coated. Refrigerate for at least 2 hours, or preferably overnight.