Wash the chicken fillets and pat them dry. Place on a baking tray and sprinkle with 2 tablespoons of oil. Season with salt and Szechuan pepper. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 15 minutes.
In the meantime, wash and peel the asparagus, cut off the woody ends. Cut asparagus into pieces and put them into boiling salted water. Cook over medium heat for about 15 minutes, drain. Clean and wash the mangetouts and cook them for about 5 minutes in boiling salted water.
Clean and wash the tomatoes and peppers. Halve the tomatoes and cut the peppers into fine, long strips. Clean and wash the cress. Wash sorrel and dab dry. Put 4 leaves aside for garnishing.
Chop the remaining sorrel. Peel and finely chop the onion. Mix vinegar with diced onion, chopped sorrel, salt and pepper. Add 3 tablespoons of oil. Mix prepared salad ingredients and marinade.
Cut the chicken fillets open. Serve salad and chicken fillets garnished with sorrel leaves.