In the crock of a large slow cooker, combine the chipotles, vinegar, lime juice, garlic, oregano, cumin, salt, pepper, and bay leaf. Stir well to combine.
In a large heavy skillet, heat the oil until shimmering. Add the beef chunks, working in batches and brown on all sides. As they are browned, transfer the meat chunks to the slow cooker.
Cook the onion in the drippings until translucent, about 5 minutes. Transfer to the crock.
Stir gently to combine the beef chunks, onions, and sauce. Secure the lid and cook for 6 to 8 hours on LOW or 4 to 6 hours on HIGH. The meat should fall apart easily. Shred the meat to your preferred texture. Serve in tacos, burritos, lettuce wraps, and bowls.
To freeze: chill the meat completely. Store the meat in an airtight container in the freezer for up to 2 months. Thaw and reheat to serve.