In a mixing bowl, toss together the chicken, celery, scallions and herbs. Set aside.
In a small bowl, whisk together the mayonnaise, lemon juice, mustard, salt and pepper. Add to the chicken and mix gently until combined. Refrigerate until ready to serve.
In a medium to large saucepan, place the parsley, thyme, onion, carrot, celery, and chicken breasts. Cover with the broth. Bring just to a boil, lower the heat to a gentle simmer and cover. Poach the chicken over very low heat for 20 minutes or until firm to the touch. Remove the pan from the heat, uncover, cool in the stock for 30 minutes.
Transfer the chicken to a cutting board and reserve the liquid. Remove the chicken from the bones and cut the meat into cubes. Discard the bones and skin.
Strain the broth and store, covered, in the refrigerator for 3 days or freeze for later use. Remove any fat from the surface of the broth before using.
Serve on a bed of lettuce with sliced tomatoes, in half an avocado or in a chicken club sandwich made with artisanal bread, crispy smoked bacon, vine-ripened tomatoes and lettuce.
Recipe copyright Television Food Network, G.P., 2001, All Rights Reserved.