The crunch of tortilla chips contrasts perfectly with this comforting Mexican soup. In addition to the chips, serve the posole with sour cream and cheese or even pomegranate seeds. Canned hominy, a natural thickener, can be found in the Latin section of the grocery store. The pork shoulder will fit snugly in your slow cooker; for ease, use turkey lifters to remove the meat from the insert, remove the bones and break up the meat, and place it back in the slow cooker (without burning your hands).
Place the first three ingredients on a small piece of cheesecloth, bundle up into a “purse,” and secure with a piece of kitchen twine. Place in the slow cooker.
Combine the next four ingredients in a small bowl. Rub the spices all over the trimmed pork. Heat the oil in a 10-inch, heavy sauté pan over medium-high heat. When the oil is hot but not smoking, add the meat and cook on the first side until golden brown, about 5 minutes. Turn over and brown the other side, about another 4 minutes. Transfer to the slow cooker, and pour the hominy on top and around it.
Add the onions and garlic to the hot pan, and sauté until softened, about 3 minutes. Add the stock, tomatillos, orange and lime juices, and jalapeños and raise the heat to high. Cook, whisking occasionally, for 5 minutes. Pour over the pork-hominy mixture in the slow cooker. Cover and cook on low until the pork is tender and cooked through, about 8-1⁄2 hours.
Carefully remove the meat from the slow cooker and place on a cutting board. Remove and discard the spice bag. Discard any bones and gummy cartilage and shred the meat. Return the shredded meat to the slow cooker and mix into the liquid. Divide the stew among serving bowls, and top each portion with diced avocado, scallions, cilantro, lime, and chips. Serve.