Heat oven to 350°. Season fish with salt and pepper and dust it with flour. Heat a large sauté pan over medium heat, add oil, and swirl to coat the bottom of the pan. Gently place the fish in the hot pan. Drop in the butter and swirl the pan so the butter melts and turns slightly brown, 2–3 minutes. Flip the fish and cook for 1–2 minutes more. Transfer the fish to a sheet pan, then place in the oven for 7–10 minutes until just cooked through.
Add sliced shallot, garlic, sausage, bok choy, and clams to the pan with the brown butter. Stir and add soy sauce and ½ cup water. Cover the pan and cook until the clams are open. Taste the broth and adjust seasoning.
To serve, divide the ingredients in the pan between 2 bowls. Top each bowl with 2 pieces of the seared cod, then garnish with chopped cilantro and fresh lemon.