If using raw chicken: poach or bake chicken breasts until cooked through (165°F internal). Let cool, then shred or dice into bite-sized pieces.
In a large bowl, whisk together mayonnaise, Greek yogurt, lemon juice, Dijon mustard, salt, and pepper until smooth.
Add the cooked chicken, dried cranberries, diced celery, sliced green onions, and chopped pecans to the bowl. Stir gently until everything is evenly coated with the dressing.
Taste and adjust seasoning with more salt, pepper, or lemon juice if desired.
Cover the bowl and refrigerate for at least 30 minutes to allow flavors to meld. Serve chilled or at room temperature on croissants, in lettuce cups, or with crackers.