Mix the mince with the egg, spice mix and some seasoning, then shape into 16 meatballs. Set aside in the fridge to firm up slightly while you make the sides.
Mix the tomatoes, coriander, ½ the garlic and ½ the lime juice in a bowl with 1 tbsp oil, season and set aside. Stir the remaining garlic into the soured cream with a handful of the grated cheese and season. Slice the avocado and squeeze over the remaining lime juice. Bring these, the taco shells and lime wedges to the table.
Heat the remaining oil in a large frying pan. Fry the meatballs over a medium heat for 8-10 mins until evenly browned and cooked through. Sprinkle over the remaining cheese, put a lid on the pan and cook for 1 min until melted, then let everyone help themselves.