Crisp water spinach stems contrast with tender leaves and soft steamed fish in this light, simple dish—which needs no more than scented rice to make a meal. The best coriander has its roots intact. If you find it, trim these and scrub with a brush, then mince and add with the sliced spinach stems. I like roasted peanut oil (Loriva is a widely available brand), which is more intense than oil from raw peanuts. If it is not available, add a soupçon of Asian sesame oil to regular peanut oil.