Pat the chicken breasts dry and season both sides generously with salt and pepper. Place a skillet over medium heat and add a splash of oil. Cook the chicken for about 6-7 minutes per side until golden brown and cooked through, then transfer to a plate to rest for 5 minutes.
While the chicken rests, toast the walnuts in the same skillet over medium heat for about 3-4 minutes, stirring frequently until fragrant and lightly browned. Remove from heat and let cool.
Finely chop the cooled chicken into bite-sized pieces. Dice the celery into small, crunchy pieces, and chop the fresh herbs finely. Squeeze the lemon juice over the celery to keep it crisp and bright.
In a large mixing bowl, combine the mayonnaise, lemon juice, and a pinch of salt and pepper. Whisk together until smooth and creamy.
Add the chopped chicken, diced celery, chopped herbs, and toasted walnuts to the bowl with the dressing. Gently fold everything together until evenly coated and well combined.
Taste the salad and adjust the seasoning with more salt, pepper, or lemon juice if needed. Let it rest for 10 minutes at room temperature to allow flavors to meld.
Serve the chicken salad chilled or at room temperature, garnished with extra herbs if desired. Enjoy the satisfying crunch combined with tender, flavorful chicken in every bite.