Lightly season the fish with a rounded ¼ teaspoon of salt. Set aside.
Put the oil into a large sauté pan with a lid and place over medium-high heat. Once hot, add the red chiles and fry for 2 minutes, stirring frequently.
Add the garlic, caraway seeds, and ancho, and continue to fry for 1 minute, until the garlic is starting to turn golden brown.
Add the tomatoes, tomato paste, sugar, and ½ tsp salt, then, once boiling, decrease the heat to medium and let simmer for 15 minutes, stirring from time to time, until the sauce is thick.
Add the fish, cover the pan, and continue to cook for 10 minutes.
To make the tahini sauce, mix the tahini and lemon juice with the water and ⅛ teaspoon salt.
When ready to serve, gently lift the fish out of the pan and set aside somewhere warm. If the fish has released a lot of liquid during the cooking and the sauce is runny, increase the heat and let it bubble away quickly until thick. Taste and add salt if needed.
Transfer the fish to a serving dish. Spoon on the sauce, sprinkle with the cilantro, and serve.
