In a small skillet, add pecans and toast on low-medium heat until fragrant and brown-ish, stirring often. Transfer to a cutting board, let cool a bit and chop coarsely.
In a large bowl, add toasted pecans, chicken, grapes, celery, parsley, red onion, mayo, mustard, salt and pepper. Stir gently to combine.
Refrigerate chicken salad for at least 2 hours as it tastes best cold.
Taste and adjust any seasonings to taste, if necessary. Serve with greens or make a chicken salad sandwich.
Notes
Store: Refrigerate in an airtight container for up to 5 days. I have not tried freezing the salad and am not sure grapes will hold up well to it.