If using leftover or rotisserie chicken, remove skin and bones and chop or shred to yield about 3 cups. If poaching, place 1 pound boneless skinless chicken breasts in a saucepan, cover with water, bring to a gentle simmer, and cook 12–15 minutes until cooked through; cool and shred.

Place the chopped/shredded chicken in a large mixing bowl.

Add the diced celery, finely diced onion, and roughly chopped cashews to the bowl with the chicken. Toss briefly to combine.

In a small bowl, whisk together the mayonnaise, Greek yogurt, Dijon mustard, lemon juice, salt, and black pepper until smooth.

Pour the dressing over the chicken mixture. Fold gently with a rubber spatula or spoon until everything is evenly coated. Taste and adjust seasoning — add more salt, pepper, or lemon juice if desired.

Stir in the chopped parsley if using. Cover and refrigerate for at least 20 minutes to allow flavors to meld; up to 24 hours.

Assembly

If you prefer the bread toasted, lightly butter one side of each slice (or brush with olive oil). Heat a skillet over medium and toast bread slices, buttered side down, until golden and crisp, 1–2 minutes per side. Alternatively, use a toaster.

Place a lettuce leaf on four bread slices (on the non-buttered side if toasted).

Spoon 3/4 to 1 cup of the chilled chicken salad onto each lettuce-lined slice, spreading evenly but keeping a slight mound in the center so the sandwich feels generous.

Top each with another slice of bread. Press gently, then cut sandwiches in half diagonally or in your preferred way.

Serve immediately, or wrap tightly and refrigerate for up to 24 hours. If storing, keep lettuce separate to avoid soggy bread and add just before serving.