Put the chicken pieces into a bowl and add the turmeric and 1 tsp salt. Put the ginger into a small blender with 1 tbsp water and blend to a paste. Squeeze the juice from the ginger over the chicken, discarding the pulp.
Mix the chicken with the ginger juice, then cover and refrigerate for a minimum of 3-4 hours or preferably overnight.
Heat the oil in a wok or a large non stick frying pan over a medium high heat. When hot, put in the red chillies, mustard seeds, urad dal, fennel seeds and cinnamon. Stir for a few seconds or until the chillies turn dark and the mustard seeds pop.
Add the garlic and stir once or twice, then add the onion and stir and saute until soft and just starting to brown. Add the tomatoes and stir and fry for 2-3 minutes until soft.
Now add the chicken with its marinade juices, the cayenne pepper and the remaining salt. Stir and fry on a highish heat until the chicken has browned- about 6 minutes.
Cover, turn heat to low and cook for another 10-12 minutes, stirring now and then until the chicken is done. Remove the cover and sprinkle in lots of freshly ground black pepper. If there is any liquid left in the pan increase the heat and dry off before serving.
Sprinkle the fresh coriander over the top and serve with tomato wedges.