In a large bowl, whisk together the mayonnaise, Dijon mustard, lemon juice and sugar with 1/2 teaspoon kosher salt and 1/4 teaspoon pepper.
Stir in the shredded chicken, grapes, walnuts, red onion and dill. Serve immediately or store in an airtight container in the fridge for up to 5 days.
Notes
The chicken: Poached chicken is my top pick for the juiciest, most tender results (here's my foolproof How to Poach Chicken guide!). Short on time? Store-bought rotisserie chicken is a great shortcut.
The walnuts: For extra crunch, stir them in right before serving rather than mixing them in ahead of time.
The red onion: If raw onion is too sharp for your taste, soak the diced onion in cold water for 10 minutes, then drain before adding.
Variations: Swap walnuts for pecans, add a handful of dried cranberries, or stir in diced celery for extra crunch.
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