Halve the chicory and remove the outer leaves. Cook the chicory in boiling salted water for 3-5 minutes. Remove, rinse in cold water and drain. Wash the fish fillets and dab dry.
Wash the tomatoes, dab dry and quarter them. Place the chicory and fish fillets in ovenproof dishes. Season with salt and pepper and sprinkle with lemon juice. Grate the Gouda coarsely and stir with crème fraîche until smooth.
Spread the Gouda mixture over the fish fillets. Add the tomatoes. Bake in the preheated oven (electric: 200 °C/ gas: level 3) for 10-15 minutes. Garnish with dill flags and serve.