Wash the fish, dab dry and cut into 2 pieces. (Defrost the frozen fish.) Sprinkle with lemon juice.
Wash, quarter and seed the tomatoes. Cut the tomatoes into strips. Peel and finely chop the onion. Clean the fennel, pick up the tender green. Wash the fennel, cut out the stalk. Cut the fennel lengthwise into thin slices.
Heat the oil in a pan (with lid). Fry the fish in it at medium heat for 2-3 minutes on each side. Season with salt and pepper. Remove the fish.
Steam the onion, fennel and tomatoes in the frying pan for 2-3 minutes. Season with salt and pepper. Pour on 100 ml water, add capers and stock. Bring to the boil. Place fish on top and steam covered for about 5 minutes.
Coarsely chop the fennel green. Arrange fish and vegetables with the stock. Sprinkle with fennel green. Add baguette.