Generously rub the lamb with salt and pepper and place in a large pot. Add enough water to reach three-quarters of the way up the sides of the meat. Add the garlic, onions, avocado leaves, oregano, thyme, epazote and parsley. Cover the meat with banana leaves and the pot with a tight-fitting lid. Place in the oven and cook until fork tender (the meat should easily pull apart and shred), approximately 3 hours. Remove the herbs and chop the meat.
Serve garnished with onions, cilantro, lime, avocado and salsa.