Toast the pecans. Add chopped pecans to a dry skillet over medium heat. Cook 3–5 minutes, stirring often, until fragrant and lightly browned.
Transfer to a plate to cool so they stay crisp.
Prep the chicken. If using rotisserie chicken, remove skin and bones, then chop or shred. For poached chicken, simmer breasts in salted water 12–15 minutes until just cooked, then cool and chop.
Mix the dressing. In a large bowl, whisk together mayonnaise, Greek yogurt, Dijon mustard, lemon juice, honey (if using), salt, and pepper. Taste and adjust the seasoning.
Add the crunch and freshness. Fold in celery, green onions, parsley, and grapes.
Stir gently to coat without crushing the grapes.
Combine with chicken. Add chicken and cooled pecans to the bowl. Stir until everything is evenly coated. If it looks dry, add 1–2 tablespoons more mayo or yogurt.
Chill for best flavor. Cover and refrigerate for at least 30 minutes.
This step lets the flavors blend and the dressing thicken slightly.
Serve your way. Spoon onto toasted bread or croissants, stuff into lettuce cups, roll into a tortilla, or serve over a bed of greens. Finish with a squeeze of lemon and extra pepper if you like.