Brick-colored, soupy casseroles flavored with sweet-spicy chili paste (kochujang) are the backbone of the Korean diet. For this seafood version, Koreans would use a light beef broth or the water left over from soaking rice. Anya von Bremzen substituted a mixture of water and clam juice.
Heat 1 tablespoon of the sesame oil in a medium enameled cast-iron casserole. Add the chili paste and stir over low heat for 30 seconds. Add the zucchini, daikon, scallions, garlic and Sesame Salt and stir until aromatic and the vegetables just begin to soften, about 2 minutes. Add the water and clam juice and bring to a boil.
Meanwhile, cut the cod into 1 1/2-inch chunks. Wrap the reserved bones in cheesecloth. When the soup boils, reduce the heat to low and add the bones; simmer for 10 minutes. Remove and discard the bones.
Increase the heat to moderate and add the cod. Cover and simmer until the fish is almost cooked through, about 2 minutes. Add the clams, cover and cook until they open, about 3 minutes.
Meanwhile, heat the remaining 1 teaspoon of sesame oil in a small skillet. Add the ground red chile and cook until fragrant, about 30 seconds. Stir the chile oil into the casserole, add the tofu and simmer for 2 minutes. Ladle into wide bowls and serve with rice.