Peel and slice the onions, peel and finely chop the garlic, and pick the coriander leaves and finely chop the stalks. Slice the chicken into 1cm strips.
Heat the oil in a pan over a medium heat and, when hot, sauté the onions, garlic, coriander stalks, spices, and whole and flaked chilli for 5 minutes, until the onion is soft but not coloured.
Add the chicken strips and cook for a couple of minutes, then add the tinned tomatoes. Bring to the boil, then reduce the heat and simmer, partly covered, for 35 to 40 minutes, or until the chicken breaks apart when pressed with the back of a spoon. Add a splash of water if it looks too dry at any stage.
Next, make the salsa. Blister the pepper and chilli skins by placing them under a hot grill or holding them with tongs over a gas flame. Once blackened all over, place in a bowl, cover with clingfilm and set aside to cool.
Roughly chop the tomatoes, put them in a colander with a pinch of sea salt and place it in the sink for 15 minutes to allow the salt to draw out some of the tomatoes’ water, then give the colander a good shake.
Peel the skins from the pepper and chilli and discard along with the seeds, then place them on a board with the spring onions and chop.
Add the tomatoes and pick over the coriander leaves and continue chopping until you have a fine salsa. Transfer to a bowl, and season with black pepper and a good squeeze of lime juice.
Shred the chicken using two forks, then drain and stir the black beans into the chilli. Continue cooking for a couple of minutes until the beans are heated through, then remove from the heat and stir in the coriander leaves.
Chop the lettuce, then serve the chilli in the tortillas with the lettuce, a good spoonful of salsa and a drizzle of yoghurt, with lime wedges on the side.