Roughly chop onions and grind them.
In a pan, fry the prawns with turmeric and salt until they are cooked. Remove and set them aside.
In the same pan, heat the oil and add the ground onions and fry them until all the rawness is gone and they become brown.
Add the ginger and garlic and fry for a minute taking care not to burn.
Add the chilli powder, garam masala powder, green chilli, soya sauce, chilli sauce, sugar and tomato ketchup and mix. Fry all this for a couple of minutes.
Add the cooked prawns and salt and mix.
Garnish with coriander leaves.