Thomasina Miers’ quick recipe for mackerel with charred spring onion salsa

Grilled spring onions are a feature of Mexican cooking, and the secret’s in being brave enough to blacken them properlyThey love to char a spring onion in Mexico: in fact, it’s virtually a national sport. Normally served sprinkled with sea salt and wedges of lime, grilled spring onions make a delicious snack, an Aztec version of edamame, if you will; but they really come into their own served alongside grilled fish or meat. We went through a phase of charring and blitzing them i