Peel the vegetable onion and cut into strips. Wash and clean the tomatoes and cut them into large pieces.
Heat 2 tablespoons of oil in a large frying pan. Fry the onions for 20-25 minutes at low heat, turning them over. After half of the stewing time, add sugar and allow to caramelize briefly. Mix in tomato paste and tomatoes.
Add wine and stock, bring to the boil once and reduce the heat again. Season to taste with salt and pepper.
Meanwhile, wash the fish, dab dry and cut into 4 pieces of about the same size. Season fish fillets with salt and pepper, turn them slightly in flour (carefully knock off excess flour).
Heat 2 tablespoons of oil in a coated frying pan. Sauté the fish on both sides for 3-4 minutes.
Cut the baguette into slices. Spread each slice with herb butter and cook in the preheated oven (electric cooker: 200 °C/ circulating air: 175 °C/ gas: see manufacturer) for approx. 5 minutes.
Remove the fish from the pan and sprinkle with lemon juice. Wash the dill, shake dry, pluck off flags and chop. Mix the dill with the onion and tomato vegetables. Arrange fish, vegetables and herb baguette on plates.