Peel, wash and cut the potatoes into pieces. Cover and cook in salted water for about 20 minutes. Add peas approx. 5 minutes before the end of cooking time, cook along.
Grate cheese. Roughly chop the walnuts. Knead both with 75 g butter. Wash the fillets, dab dry. Fry them briefly on each side in 1 tablespoon of hot oil. Season with salt and pepper. Remove and place in an ovenproof dish.
Spread cheese-nut butter on top. Bake in the preheated oven (electric oven: 200 °C/circulating air: 175 °C/gas: level 3) for approx. 20 minutes.
Mix vinegar, mustard, honey, salt and pepper. Stir in 4 tablespoons of oil vigorously. Peel onion, chop finely and stir in. Wash and peel the cucumber, if necessary, and slice it in fine slices directly into the vinaigrette.
Wash mint, shake dry. Pluck off the leaves and cut finely. Heat milk and 2 tablespoons of butter. Drain potatoes and peas, add milk. Mash everything finely. Season the puree with salt and nutmeg, stir in the mint.
Season the cucumber salad to taste again. Serve with chicken filets and puree. Drink tip: white wine, e.g. a Sauvignon blanc.