Wash the tomatoes and cut into thick slices. Clean and wash spring onions and cut them into thin rings. Wash thyme, dab dry and chop coarsely. Wash lemon hot, dry and cut in half.
Squeeze one half and cut the other into thin slices.
Wash the fish, dab dry and cut into 4 pieces. Sprinkle with lemon juice and leave to stand for 5-10 minutes.
Preheat oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3). Cut off 2 pieces of parchment paper of approx. 30 cm length. Place tomato slices in the middle of the paper. Season with salt and pepper. Dab the fish dry, place the lemon slices on top and season as well.
Sprinkle with spring onions and thyme. Sprinkle with oil. Fold parchment paper tightly together and place on a baking tray. Bake in a hot oven for about 20 minutes. Cut the baguette into slices and add to the bread.