Soak the basmati rice for 30 minutes in cold water. Drain well.
Heat the oil in a large saucepan and add the mustard seeds. Fry the seeds until they pop and then stir in the turmeric. Fry for another minute and add the rice, water and salt. Bring to the boil uncovered, then turn the heat down low, cover and simmer for 15 minutes. Don't open the lid or stir the rice.
Remove the saucepan from the heat and let it sit for 10 minutes.
Before serving add grated lemon zest and lemon juice.
Fluff the rice with a fork and serve.
Black mustard seeds provide a nutty flavour when fried and tend to be far more pungent than the white mustard seeds.