Make the dressing: In a small bowl, whisk together the Greek yoghurt, Dijon mustard and lemon juice. Season with salt and pepper to taste. Tip: If using rotisserie chicken, wait to add salt until after the salad is fully assembled and tasted, as rotisserie chicken is often already well seasoned.
Shred the chicken: If not already shredded, use two forks to pull the cooled chicken into bite-sized pieces (alternatively roughly chop). Transfer to a large mixing bowl.
Assemble the salad: Add the grapes, celery, green onions, parsley, apple and toasted walnuts to the bowl with the chicken.
Combine: Pour the dressing over the salad ingredients and gently fold everything together until evenly coated. Adjust seasoning as needed.
Serve: Spoon over a bed of crisp salad leaves or tuck generously into sandwiches. Enjoy!
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