Cook or prep the chicken: Use rotisserie chicken for speed or poach 1.5 pounds of chicken breasts in lightly salted water until just cooked through. Cool completely, then dice or shred into bite-size pieces.
Toast the nuts: Warm a dry skillet over medium heat.
Add nuts or seeds and toast, stirring, until fragrant and lightly golden, 3–4 minutes. Let cool to keep them crisp.
Make the dressing: In a large bowl, whisk Greek yogurt, light mayo (if using), Dijon, and lemon juice. Season with 1/2 teaspoon salt and 1/4 teaspoon black pepper to start.
Taste and adjust.
Prep the mix-ins: Finely chop celery and onion. Dice the apple last so it stays fresh. If you like, toss the apple with a splash of lemon juice to prevent browning.
Combine: Add chicken, celery, onion, apple, and herbs to the bowl with the dressing.
Fold gently until everything is well coated.
Finish with crunch: Stir in most of the toasted nuts, saving a few for sprinkling on top right before serving.
Adjust seasoning: Taste and add more salt, pepper, or lemon as needed. If you want more zip, add a pinch of celery seed or paprika.
Chill: Cover and refrigerate for at least 20–30 minutes. This helps the flavors blend and the texture set.
Serve: Spoon over greens, tuck into a wrap, or pile onto toasted whole grain bread.
Finish with the reserved nuts and extra herbs for a fresh look.