If using fresh sweetcorn, wash and simmer it in a pan of water for 5-10 minutes until tender, then drain and set aside. If using frozen sweetcorn, simmer for 15 minutes, then drain and set aside.
Meanwhile, place the coconut and half the cashew nuts in a grinder with 200 milliliters / 4.5 cup of water. Process for 5 minutes, then set aside.
Heat the oil in a large saucepan an add the mustard seeds. As they begin to pop, add the green chillies, ginger and curry leaves. Lightly saute for about 2 minutes, stirring. Add the onions and cook until golden brown. Add the tomato paste, chilli powder, turmeric, a little salt and the ground coconut mixture. Mix well and cook for 5 minutes over a low heat. Add the bell peppers and cook for 2 minutes, then add the cooked sweetcorn and the remaining cashew nuts and cook for a further 5 minutes. Remove from the heat and serve hot, with indian breads (naan, chapatti, paratha etc).