How to Make It
Preheat the oven to 375°. In a large enameled cast-iron casserole, heat 2 tablespoons of the canola oil. Season the lamb with salt and pepper. Add 4 shanks to the casserole and cook over moderately high heat, turning, until browned all over, 7 to 8 minutes; transfer to a baking sheet. Repeat with the remaining canola oil and lamb shanks.
Add the garlic and half each of the onion, celery and carrots to the casserole; cook, stirring occasionally, until golden, 5 minutes. Stir in the cinnamon, oregano, 1 teaspoon of the cumin and the chopped chiles. Add the shanks and any juices. Add the stock and bring to a boil. Cover and braise in the oven for 2 hours, until the lamb is very tender.
In a heatproof bowl, cover the remaining chiles with 2 cups of boiling water; soak for 30 minutes. Transfer the chiles and 1 cup of the liquid to a blender; puree until smooth.
Transfer the lamb to a baking sheet and loosely tent with foil. Strain the broth, discarding the solids. Skim off the fat. Wipe out the casserole.
Heat the olive oil in the casserole. Add the remaining onion, celery and carrots and cook over moderate heat, stirring occasionally, until golden, about 5 minutes. Stir in the chile puree, coriander, hominy, pinto beans and the remaining 1 teaspoon of cumin and cook for 2 minutes. Add the broth and simmer for 10 minutes. Stir in the lime juice and season with salt and pepper. Add the shanks to the pot and cook just until heated through. Serve the posole in bowls, passing cilantro, avocado and lime wedges at the table.