In a bowl, add the pork shoulder steaks, cumin powder, coriander powder, paprika, smoked paprika, Mexican oregano, sea salt, black pepper and sunflower oil. Mix thoroughly. Cover and set aside in the fridge for at least 2 hours, up to 24 hours.
Heat a pot over a medium-high heat. Add the pork far or lard and heat for 1 minute. Place a marinated pork shoulder steak in the pan and allow to sear for 2 minutes on each side until nicely browned. Set the browned pork steak aside on a plate and repeat until all of the steaks are browned.
Return all of the seared pork shoulder steaks to the pot, add the garlic, onion, light chicken stock and fresh lime juice. Bring to the boil, reduce the heat to low and simmer the pork for 1 hour and 40 minutes, turning the steaks once or twice during this time.
Use tongs to remove the pork meat from the cooking liquid - it should be very tender and easy to pull apart. At this stage, the meat can be served immediately or set aside to cool completely and stored in the fridge for 2 days or in the freezer for 3 months (see notes for cooking ahead / reheating advice).
Warm your tortillas and layer them (2 small tortillas per taco) on a serving plate. Top generously with the pork and add your favourite combination of toppings and / or hot sauces.
If preparing ahead of time, I like to let the meat and the cooking liquid / fat cool down and then store them together. The fat will set in the fridge and the meat will resemble a terrine - you can simply slice the desired quantity of meat / fat and slowly reheat it in a pot with a little water for 10-12 minutes until the pork meat is fully heated through.
Mexican oregano is from a different plant family from the oregano you know and love on your favourite pizza. Native to Mexico, it has a very desirable citrus flavour.