Prick the aubergines all over with a fork, then set over a medium gas flame (or on the coals of a barbecue or under the grill) and cook, turning occasionally with tongs, until blackened and collapsing, about 20-25 mins. Transfer to a plate and leave to cool. Peel the skin from the cooled aubergines or scoop out the flesh using a spoon. Try to remove most of the skin, but don’t worry if a few flecks remain.
Heat the oven to 200C/180C fan/gas 6. Heat the olive oil in a large ovenproof frying pan with the bay leaf and cumin seeds. When they start to sizzle, add the onion and garlic. Fry for about 5 mins until fragrant but not coloured, then stir in the tomato purée and cook it down for a couple of mins.
Add the tomatoes and dried oregano, and cook for a few mins more until they have collapsed into the sauce. Add the aubergine flesh, chilli powder, chilli flakes and vinegar, and cook, stirring, for 1 min, then tip in the cans of black beans, one drained and one still with its liquid. Squeeze over a little of the lime juice and cook for 5 mins until reduced and bubbling, then transfer to the oven and roast for 15-20 mins until deep, dark and fully reduced.
Season with more lime juice, if you like, and spoon the aubergine mixture into the warm tortillas with the coriander, crumbled feta, lettuce and pink pickled onions to serve