Remove the meat from the package and rinse it, then dry it using paper towels. Cut it into two or three pieces, depending on the size of the cooking pot you're using; the parts should be more or less the same size so they can cook evenly.
Place the meat pieces, bones, onion, garlic, bay leaf, and avocado leaves (if using) in a large cooking pot. Cover with water and cook until the meat is very tender and you can easily shred it. If using a regular stock pot to cook on the stove, the meat will be ready in about two and half hours. In the slow cooker, it will take 8 hours in the low setting and 6 hours in the high setting. It will take 50 minutes in a pressure cooker, or 40 minutes in an Instant Pot.
While the meat is cooking, lightly toast the peppers for a few seconds on the griddle, then place them in a saucepan with hot water and let them soak for 20-30 minutes until they're very soft.
Drain the peppers and place them in your blender with the two garlic cloves, oregano, and 1 cup of the cooking broth (or clean water). Process until you have a smooth sauce.
Remove the cooked meat from the pot. Discard any fat and shred the meat.
Heat the oil in a large frying pan and pour the sauce in. Fry the sauce for a few minutes, then stir in the shredded meat. Let it cook for about 5-8 minutes to allow all the flavors to combine. Season the stew with salt and pepper.
Serve with warm corn or flour tortillas, chopped onion and cilantro, and green salsa. You can serve it with raw or cooked green salsa.