1. Put the celery, carrot, onion, and chicken breast in boiling water. Cook for 15 minutes.
2. In another pot, bring salted water to a boil, adding a few drops of red wine vinegar. Add the mushrooms and cook for 3 minutes.
3. Drain the chicken and mushrooms. Cut them into thin slices.
4. On each plate, arrange a slice of chicken and a slice of mushroom in alternating order. Sprinkle with a few pine nuts.
5. Mix the extra virgin olive oil with the balsamic vinegar and pour over the salad. Serve.