Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3). Wash and halve the fish. Sprinkle with lemon juice. Place bread in 3 ovenproof baking dishes, drizzle with 1 tablespoon of oil
Roast in a hot oven for about 6 minutes. Heat 2 tablespoons of oil in a frying pan. Fry the fish on each side for about 3 minutes. Peel and chop onion. Wash and halve mushrooms and tomatoes
Season the fish and put it on the bread. Fry the onion and mushrooms in 1 tablespoon of hot oil. Fry the tomatoes briefly. Season with salt, pepper and herbs and spread on the fish
Drain the mozzarella and sprinkle over it. Bake everything in a hot oven for about 8 minutes. Serve with rocket salad