To make the barbacoa marinade, put all the dried chillies in a bowl with 250ml hot water and leave to rehydrate for 12 hrs. Once soft, drain the chillies into a jug or bowl, reserving the soaking water. Remove the stems. Pour the reserved water into a blender and add the chillies and the garlic. Blend until smooth. Add the salt, balsamic vinegar and avocado leaves and blend again until smooth. Gradually add the grapeseed oil, with the blender running on a low speed, until the sauce emulsifies. Taste for seasoning and adjust accordingly – the marinade should be on the salty side.

Pat the lamb shanks dry with kitchen towel and lightly score with a sharp knife. Put the meat in a bowl and coat thickly in the barbacoa marinade. Cover and chill for 12 hrs.

Wipe the banana leaves and quickly heat in a non-stick pan, or under the grill, until they change colour and turn shiny. Arrange in the bottom of a large, deep roasting tray in a few layers, leaving enough for the sides. You will use them to wrap around the shanks.

Heat the oven to 200C/180C fan/gas 6. Put the stock, garlic, onions and tomatoes in the bottom of the roasting tray on top of the banana leaves. Put the marinated lamb on top, then wrap tightly in the remaining banana leaves. Cover with two layers of foil to seal the meat in well – this will help keep in all the steam. There should be no holes, gaps or tears in the foil. Cook for 4 hrs.

Remove the foil and banana leaves covering the meat. Carefully move the lamb onto a tray and leave to cool completely. Strain the remaining stock into a large pot, and put over a high heat to bring to the boil. Reduce to a medium heat and cook the liquid until it has reduced by a third. Check for seasoning and adjust accordingly, adding more dry chillies for a spicier broth.

Meanwhile, make the avocado salsa. Whizz all ingredients except the avocado in a blender with 1 tsp salt until smooth. Taste and adjust seasoning and spiciness if needed, then add the avocado and blend again until smooth.

Shred the cooled meat and mix with a little bit of the cooking juices. Lightly fry the corn tortillas for a few seconds on each side in a dry non-stick pan to make them soft and malleable. Spoon some of the meat into the middle of each tortilla, then roll into a cigar shape. Pin each top and bottom with the toothpicks to hold them together.

Fry the tacos in a little more oil for 2-3 mins, or until crisp. You may have to do this in batches. Put the cooked rolls onto a plate lined with kitchen paper whilst you finish frying the rest. To serve, arrange them on a plate and top with the Mexican crema or soured cream, the queso fresco or feta and the avocado salsa, finishing with the shredded lettuce.