Preheat the oven to 220°C, fan ventilation and rack in the middle of the oven.
Place a large pot filled with salted water on high heat and bring to a boil. Add the potato slices and bring back to the boil, cooking for 5’ with the lid on. Remove from the pot and allow to cool.
Take a large oven proof dish and lightly brush with olive oil. Place the potato slices in the middle of the dish for the fish to sit on, leaving some space on the top and bottom sides of the dish where next you add the peppers, fennel and oregano.
Add the anchovies and tomatoes all-over the potatoes and pour on top the diluted saffron and the chicken broth. Drizzle with ¾ of the oil and season with the salt and pepper while taking care with the salt as the anchovies are already quite salty. Place in the oven and cook for 35’.
Remove from the oven and add into the belly of the fish the lemon slices, slit diagonally the flesh of one side of the fish and rub with the remaining oil. Season with salt and pepper and place over the potatoes and tomatoes with the slit side facing upwards. Reduce the temperature to 200°C and cook for 45’.