Heat the oil in a frying pan, add the onion and fry until it is golden brown or caramalised- this should take 8-10 minutes.
Add the garlic, salt, turmeric, cumin, coriander, chilli powder and tomato puree and stir for 30 seconds then tip in the prawns and stir fry for 2 minutes.
Add 65 ml water and cook for a minute more. Remove from the heat and sprinkle over the garam masala and the coriander leaves.