Mix the vinegar with turmeric, chilli powder, salt and pepper and mix to a paste.
Wash the chicken, then pat dry with kitchen paper then massage with the marinade. Leave in the fridge for couple of hours.
For the curry:
In a frying pan, on a medium heat add the oil, and mustard seeds. Wait until they start to splatter then add the Fenugreek seeds, curry leaves, onions then brown for a few mins, add the garlic and ginger and mix well and fry.
Now everything is nice and brown and you have this beautiful aroma, add the chopped tomatoes and cook on a low heat for 5 or 10 mins.
Add the marinaded chicken and fry for 15 mins but keep tossing.
Add the spices with the water then add to the chicken. Mix well, cover and cook for 20mins then add the peas. Cover and cook on a low heat or until the chicken is cooked, about 20 mins more.
Turn off the heat, chop a few fresh coriander leaves and scatter over the chicken. Serve with your choice of salad.
You can add more water if you need it, but I like this curry a little dry.