1. Arrange pecans in a single layer on a baking sheet.
2. Bake at 350° for 5 to 7 minutes or until lightly toasted. Cool pecans on a wire rack 15 minutes or until completely cool.
3. Whisk together mayonnaise and next 5 ingredients in a large bowl; stir in pecans, chicken, celery, and onion just until blended. Stir in grape halves, if desired. Garnish, if desired.