Begin by poaching the chicken breasts in a pot of simmering water for about 15-20 minutes, or until they reach an internal temperature of 165°F. Once cooked, remove the chicken from the pot and let it cool slightly. Dice the poached chicken into 1-inch cubes.

In a large mixing bowl, combine the diced chicken, halved red grapes, chopped pecans, diced celery, and sliced green onions. If using the optional fresh tarragon and parsley, add them now as well. Gently toss to meld the flavors.

In a small bowl, whisk together mayonnaise, Dijon mustard, olive oil, lemon juice, salt, and pepper until smooth. Adjust seasoning if necessary.

Pour the dressing over the chicken salad mixture in the large bowl. Gently fold the dressing into the salad, ensuring all are well-coated without breaking the chicken pieces.

For optimal flavor, cover the salad and refrigerate for at least 1 hour before serving.

Serve the Chicken Salad either on a bed of greens, or use it as a filling for croissants or sourdough bread.