In a large, deep skillet, melt the butter in 2 tablespoons of the olive oil. Add the onion, artichoke hearts, shiitake caps, carrots and garlic and cook over moderately high heat, stirring occasionally, until lightly browned, 7 minutes. Add the chickpeas and stock, season with salt and pepper and bring to a boil. Simmer over low heat until the vegetables are tender and the liquid is nearly evaporated, 5 minutes. Stir in the parsley and chives and keep warm.
In a large nonstick skillet, heat the remaining 2 tablespoons of olive oil until almost smoking. Season the cod fillets with salt and pepper, add to the skillet and cook over high heat until well browned on the bottom, about 6 minutes. Carefully flip the fillets and cook until they're white throughout, about 3 minutes longer.
Spoon the vegetables into shallow bowls and top with the seared cod fillets. Serve with lemon wedges.
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