Spray a large saucepan with the vegetable cooking spray over medium high heat. Add the onions and saute, stirring often, for about 5 minutes. Add the garlic and chilli powder and saute for 2 more minutes.
Then add the chicken stock, chilli peppers and cumin, stirring well. Bring to a boil, reduce heat to low, cover and simmer for 20 minutes.
Next, add the tomatoes, green capsicum, prawns and cod. Return to a boil then reduce heat to low, cover and simmer for another 5 minutes. Gradually stir in the yoghurt until heated through.