Make the salsa: Halve the tomatoes, then squeeze out and discard the seeds – this seems a bit wasteful, but it really intensifies the flavour of the salsa. Finely chop the tomato flesh and onion. Halve, seed and finely chop the chilli. Mix the tomato, onion and chilli in a bowl with the coriander and some salt and pepper. At this point the salsa can be covered and chilled for up to 2 days, but bring it back to room temperature before serving.
Cook the lamb: Season the lamb steaks on both sides and rub with a little olive oil. Barbecue or cook on a hot griddle for 3-4 minutes each side for medium, a little longer if you prefer your lamb well done. Serve each leg steak with a dollop of the salsa, new potatoes and a big crunchy salad.