Heat the cooking oil in a wok or frying pan.
Saute the onion, garlic, ginger, tomato and chilis until fragrant, about one minute.
Arrange the fish fillets in a single layer on top of the sautéed vegetables. Drizzle with fish sauce.
Pour in the coconut cream. Bring to a simmer then lower the heat and continue simmering, uncovered, for about seven minutes.
Turn off the heat, taste the sauce, if it needs more fish sauce, then add more. Or just serve extra fish sauce on the side.
Scoop out the fish fillets and arrange on a serving platter. Pour the sauce around them. Sprinkle with sliced scallions and serve with hot rice.