Place the aubergines into a bowl, add a little oil and the lime juice and season with plenty of salt. Toss well to ensure even coating of the oil.
Heat a griddle pan until smoking. Add the aubergines and chargrill in batches, turning once, until cooked and marked with lines from the griddle. Remove each batch from the pan and keep warm.
For the nuoc cham, place the chillies and garlic into a food processor and blend to a paste. Add the lemon juice, rice wine vinegar and water and blend again until smooth.
For the cumin yoghurt, dry-fry the cumin seeds in a hot frying pan, until turning dark brown and fragrant, then crush the cumin with a pestle and mortar.
Place the yoghurt into a serving bowl and stir in the crushed cumin.
To serve, arrange the aubergines onto six plates. Spoon some nuoc cham dressing over each plate of aubergines and top with a dollop of the cumin yoghurt.