Heat the oil in a wide, non-stick covered pan. Add the onion, put on the lid and cook for 5 mins, stirring occasionally, until golden. Add the whole and ground spices, the ginger and garlic, stir for about 30 secs to release their flavours, then pour in the tomatoes and a can of water, the chickpeas and stock cube. Cover and leave to cook for 20 mins.
Stir in the tamarind (if using), add the mackerel, then cover and cook for 8 mins more. Meanwhile, heat the rice following pack instructions, then tip into a bowl and toss with the almonds and coriander. Serve with the curry.