Combine the Spice Mix ingredients in a bowl and mix well. Sprinkle over the beef chuck roast pressing to adhere.
Heat the olive oil in a large heavy-based pot over high heat. Add the beef (in batches if necessary) and brown well on all sides. Remove onto a plate.
Turn heat down to medium. If the pot looks dry, add more avocado oil.
Add the garlic and onion and cook for 3 minutes until soft. Stir in the chipotle pepper and sauce.
Add the orange juice and lime juice, and scrape the pot’s bottom, so the brown bits mix into the liquid.
Add diced tomato and the juice, beef stock, stir and then return beef into the pot.
Bring to a simmer placing a lid on top, cook for 2 hours.
Remove the lid and simmer for another 30 minutes until beef is tender enough to shred.
Remove the beef and shred.
Leave the sauce to simmering with the lid off for 10 to 15 minutes to reduce and thicken. Add salt to taste.
Place shredded beef back into the sauce.
Transfer beef into a large dish and serve. It can be used for any Mexican dish…tacos, burritos, enchiladas, whatever you fancy.