Heat the oil in a large, nonstick wok or frying pan. Add the onion and stir-fry over a medium heat for 5–6 minutes until softened.
Pound the mustard seeds with the garlic using a pestle and mortar and add to the pan. Stir-fry for 1 minute, then add the turmeric, ground coriander and curry powder. Stir-fry for 2–3 minutes, then add the chicken. Stir-fry over a high heat for 5 minutes, then add the measured water. Season well.
Bring to the boil, cover tightly and reduce the heat to low. Cook gently for 20–25 minutes, stirring occasionally until the chicken is cooked through. Remove from the heat and stir in the yogurt.
Serve immediately with pilau rice and garnished with coriander leaves.