Lemon cod with spinach-and-potato stew

Instructions

1. Sprinkle both sides of the cod with the salt and pepper. Heat 1 teaspoon of the oil in a large nonstick skillet over medium-high heat. Add the cod and cook until it is just opaque in the center and browned on the outside, about 3 minutes on each side. Transfer to a plate; set aside.
2. Heat the remaining 2 teaspoons oil in the same skillet, then add the onion and garlic. Cook over medium-low heat, stirring occasionally, until the onion is very tender, about 8 minutes. Add the tomato; cook until soft, about 5 minutes. Add the potatoes, broth, lemon zest, and lemon juice; bring to a boil. Reduce the heat and simmer, covered, until potatoes are fork-tender, about 15 minutes.
3. Meanwhile, whisk together the water and flour in a small bowl until smooth. Stir mixture into the simmering vegetables. Add the spinach. Cook, stirring constantly, until the sauce thickens and the spinach begins to wilt, 2–3 minutes. Return the cod to the skillet; heat through.