Clean, wash and cut the spring onions into rings. Wash, clean and slice the mushrooms. Cut tomatoes crosswise, blanch, remove and peel the skin.
Cut the tomatoes into quarters and remove the seeds. Then cut the tomatoes into slices. Wash and finely chop the thyme, tarragon (except for 4 sprigs) and parsley. Mix vegetables and herbs and season with salt and pepper.
Peel and crush the garlic and add it. Wash the fish and dab dry. Put a slice of lemon and a sprig of tarragon in each fish. Pour the vegetables into an ovenproof dish. Place the fish on top.
Pour white wine over it. Cover the mould with aluminium foil and cook in the preheated oven (electric cooker: 225 ° C/ gas: level 4) for 30 minutes. Remove the aluminium foil 10 minutes before the end of the cooking time. Garnish with parsley.