How to Make It
In a large, deep skillet, combine the fish bones with the tomatoes, ginger, scallions, cilantro, tomato paste and sambal. Add 6 cups of water and set a bamboo steamer on top. Bring the water to a boil, then simmer over moderate heat until the tomatoes start to break down, about 5 minutes.
Drizzle the fish with oil and season with salt. Put the fish in the steamer basket skin side up, cover and steam over moderately low heat until just cooked through, 5 to 7 minutes.
Using a thin spatula, transfer the fish to shallow bowls. Strain the broth into a heatproof bowl; discard the solids. Season the broth with salt and ladle over the fish. Pile the cucumber alongside, garnish with sesame seeds and serve.