Put the onion, garlic and ginger in a food processor or blender and purée. (Alternatively, finely chop the ingredients and mix well together.)
Heat the oil in a saucepan. Add the onion purée and the chilli, then sauté over a low heat for about 7 minutes or until the mixture is beginning to turn golden brown in places.
Add the mustard seeds, ground coriander, cumin and turmeric, then stir to form a paste. Gradually pour in the stock, water and tomatoes, stirring well. Bring to the boil, then reduce the heat and cover the pan. Simmer over a low heat for 10 minutes or until the spices are cooked and their flavours blended.
Add the okra, potatoes, capsicum, raisins and pepper to taste. Stir well, then cover again and simmer over a low heat for 15–20 minutes or until the potatoes are tender.
Stir in the chopped coriander and serve at once, sprinkled with extra coriander leaves to garnish.