Clean, clean and slice the mushrooms. Clean and wash spring onions and cut them into rings. Mix cream cheese with mushrooms, spring onions and egg yolk. Season with salt, pepper and 1 tablespoon lemon juice.
Wash the fish, dab dry and season with salt and pepper. Place them side by side in a greased casserole dish, spread with cheese cream. Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 20 minutes.
Wash the dill, dab dry and chop. Wash and clean the cucumber and cut into thin slices with a vegetable slicer. Mix 1 tablespoon lemon juice and 1 tablespoon water with sugar, salt and pepper, fold in oil.
Stir in the dill. Arrange fish and cucumber salad on plates, garnish with lemon wedges and dill. Serve with baguette.