For the lamb neck barbacoa:
- Preheat oven to 325 degrees. Begin charring wood chips in a small sauté pan. (Be sure to turn on the hood vents.)
- While the chips are charring, rub each lamb neck with 1 tablespoon salt and ½ cup of the pasilla marinade. Wrap each lamb neck in the banana leaves several times over. (This step can be omitted, but the dish will not have quite the same flavor.) Place lamb necks in a roasting pan with enough room to hold lamb and the sauté pan with wood chips.
- Prepare aluminum foil to seal off roasting pan. As soon as wood chips are smoking, add sauté pan into the roasting pan and quickly seal with foil to trap in the smoke. Place in oven and cook until lamb is tender and falling off the bone, about 4 hours.
For the pickled red onions:
Place onion in a nonreactive container and set aside. In a small pot, bring vinegar and water to a boil. When boiling, pour over red onion and let cool to room temperature uncovered.
For the mint salsa verde:
- Bring a pot of water to a boil to blanch the herbs. Prepare an ice bath. When water reaches a boil, add mint and cilantro and cook for about 7 seconds. Remove herbs with a slotted spoon and quickly drop into ice water. This will stop the cooking and helps give the salsa its bright green color. After the herbs are thoroughly chilled, remove from water, squeezing out excess.
- Cut open avocado, remove pit, and scoop flesh into a blender. Add blanched herbs and salt. Begin pureeing, slowly drizzling in avocado oil. Add ice water as needed to achieve desired consistency. Adjust seasoning to taste.
- When the lamb is tender, remove from the oven and allow to cool slightly. When cool enough to handle, begin pulling off the meat, discarding any tendons you might find. When you have all the meat shred into smaller pieces, lightly season with salt and keep warm while you prepare the tortillas.
- Heat tortillas in an un-greased sauté pan until hot and wrap in a clean dishtowel to keep warm until ready to serve.