1.Wash and clean the cilantro and finely chop the Serrano pepper
2.Juice the lemon. Do not use bottled lemon juice.
3.In a food processor, place the cilantro and serrano pepper and process till coarsely chopped. Push down the paste on to the blades till it is finely chopped.
4.Add plain Greek yoghurt and lemon juice to the processor and process till completely combined.
5.Add cumin and mustard to the processor, season with salt and pepper and process till blended. Set aside to chill before serving.
6.Serve chilled as a dip with tandoori chicken.
•Add two cloves of garlic if you like the taste.
•If you want a spicier version, use local chilies with the seeds.