1Preheat the oven to 160°C (fan-forced) or set up your slow cooker.
2Heat the olive oil in a large, ovenproof frying pan over medium–high heat. Add the beef brisket and sear on all sides until browned, then remove and set aside.
3Add the onion and garlic to the same pan. Sauté for 2–3 minutes until starting to soften. Stir in the oregano, paprika, and tomato paste and cook for another minute.
4Add the crushed tomatoes, chipotle peppers, stock, and sugar, stir well, and bring to a simmer.
5Return the beef to the pan, ensuring it is mostly submerged in the sauce. Cover with the lid and transfer to the oven. Cook for 4 hours, turning the beef halfway through, until it is tender and easily pulled apart. Alternatively, transfer everything to a slow cooker to cook for up to 8 hours.
6Remove the beef. Shred it with two forks, then return it to the sauce and stir to coat.
7Dunk the tortillas in the slow cooker beef juice and place them in the pan.
8Add some shredded beef and cheese to each tortilla.
9Fold the tortillas and let them cook until gooey and crispy.
10Meanwhile, blend all the avocado dipping sauce ingredients until smooth. Adjust the seasoning to taste.
11Serve the crispy mini tacos with avocado dipping sauce.