Preheat the oven to 180C. Scatter the walnuts onto a baking tray and roast for 5-10 minutes until a deep golden brown. Tip the nuts into a tea towel and rub well to remove as much skin as possible. Chop the walnuts finely and toss in a sieve to remove any remaining skin and dust.
Put all the ingredients into a large bowl and mash everything together thoroughly with a fork. Taste and adjust the seasoning.
Note For strained yoghurt, spoon 1kg thick natural yoghurt into a clean muslin square or tea towel. Tie the corners together and suspend from a wooden spoon over a deep bowl. Refrigerate overnight to drain.