Bring the water and rice to a boil in a pot. Cover, reduce heat to low, and simmer 45 minutes.
Heat the oil in a skillet over medium-high heat. Stir in the onion and garlic, and cook 1 minute. Mix in cod, and season with curry powder, chili powder, turmeric, cumin, salt, and pepper. Pour in the coconut milk, and mix in frozen vegetables. Cover, and cook 10 minutes, or until vegetables are tender and cod is easily flaked with a fork.
Drain 1/2 cup liquid from the skillet into a bowl, and mix with cornstarch. Stir back into skillet to thicken sauce. Serve over the cooked rice.