Bring the water and rice to the boil in a pot. Cover, reduce heat to low, and simmer 45 minutes.
Heat the oil in a frying pan over medium-high heat. Stir in the onion and garlic, and cook 1 minute. Mix in cod, and season with curry powder, chilli powder, turmeric, cumin, salt and pepper.
Pour in the coconut milk, and mix in vegetables. Cover, and cook 10 minutes, or until vegetables are tender and cod is easily flaked with a fork.
Drain 125ml liquid from the pan into a bowl, and mix with cornflour. Stir back into pan to thicken sauce. Serve over the cooked rice.