Place the chicken breast in a pot and cover with water and a generous pinch of salt. Bring to simmer, cover and cook for 15-20 minutes until cooked through. Remove the chicken from water and let rest until cool enough to handle. Use a stand mixer with the paddle attachment or two forks to shred the chicken. Let cool completely before tossing with the other ingredients.
Whisk together all of the dressing ingredients in a large bowl. Next stir in the onion, pecans, grapes, celery, and chicken. Season to taste with salt and pepper.
If you want to use a rotisserie chicken to make this salad, remove the breasts from bird and shred as you normally would. Save the carcass and the rest of the meat for another recipe like tacos or chicken soup!