In a blender, combine buttermilk, onion, garlic, oregano, corander, cumin, cardamom, salt, and pepper -- blend well. Pour buttermilk mixture into a gallon-sized Ziploc® bag with the cilantro and massage bag to mix.
Add skirt steak to the marinade in the bag making sure to coat steak. Remove as much air from bag as possible and lay in the refrigerator for 4-5 hours, or up to 24 hours, rotating bag occasionally to be sure steak is well covered.
An hour before grilling, remove the steak from the refrigerator and allow to come to room temperature. Light a grill or preheat a grill pan. Grill the steak over med-high heat until seared on the outside and medium-rare within, about 5 minutes on each side depending on the thickness of the steak (thinner steak will take less time). Transfer the steak to a cutting board, tent with foil, and let rest for 8-10 minutes.
Thinly slice the steak, cutting across the grain--you may need to rotate the steak and cut from another edge if the strips get too long (it's okay if the pieces aren't exactly the same size). Serve in warm tortillas and garnish with cabbage, fresh avocado, Pico, Habanero-Cilantro Sauce, and fresh lime wedges.
*Prep time includes marinating time.Skirt steak cooks quickly, so it is best to have the garnishes and side dishes done before cooking the steak.Nutritional information includes recipe ingredients only. Garnishes figured separately.