Halve the cucumber lengthways and scoop out the watery seeds with a teaspoon, then slice into thin half-moons. Slice the red onion very finely.

Toss the onion with the lime juice, salt and sugar first and leave it for 10–15 minutes. This lightly pickles it and takes away the harsh raw-onion edge.

Just before serving, add the cucumber, chilli, coriander and cumin. Toss and taste—you want it noticeably tart and fresh, not sweet.

If you have chaat masala, a small pinch at the end is excellent, but don’t overdo it; the salad should remain a clean counterpoint to the lamb rather than becoming another heavily spiced component.

I’d make the onion/lime mixture ahead, but don’t add the cucumber until perhaps 10–15 minutes before 6, otherwise it starts shedding water.