Wash and clean the cucumber and cut into large cubes. Wash cod fillets, dab dry and sprinkle with lemon juice. Season with salt and pepper. Put the cod fillets in an ovenproof dish and pour on the hot broth. Coarsely grate the cheese, mix with the cucumber cubes and spread on the cod fillets. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 15-20 minutes. In the meantime, clean, wash and drain the lamb's lettuce.
Wash, clean and quarter the tomatoes. Halve quarter crosswise. Peel shallot and dice finely. Season vinegar with salt, pepper and sugar. Stir in oil bit by bit. Mix the tomatoes, lamb's lettuce and shallot with the vinaigrette. Arrange the cod fillets with the tomato lamb's lettuce on plates and garnish with dill flags