If you like more of a kick, add a pinch of chilli flakes and half a teaspoon of hot smoked pimentón to the escalivada instead of the red chilli.
Heat the oven to 210C (190C fan)/410F/gas 6½. Prick the aubergine all over with a fork and put it in a roasting tin with the peppers, tomatoes, onion wedges, garlic and chilli.
Season generously, add the olive oil, toss to coat, then scatter over the fresh herbs.
Roast for an hour, until all the vegetables are charred and very tender.
Peel off and discard the skin from the aubergine and peppers, and scrape out the pith and seeds from inside the peppers, saving as many of the cooking juices as possible.
Tear the aubergine and pepper flesh into rough strips and return them to the oven tray.
Squeeze the garlic out of its papery skins, and add the soft flesh to the tin, too.
Pour the sherry vinegar and extra-virgin olive oil all over the roast vegetables, then toss to coat.
Put a little oil in a griddle or large frying pan on a medium-high heat.
Season the mackerel on both sides, then fry the fillets skin side down for two to three minutes, until crisp.
Flip over, fry for just a minute or two more, until just cooked through, then serve with the warm escalivada and some crusty bread to mop up all those lovely juices.
