1. Preheat oven to 350°. Bake pecans in a single layer on a baking sheet 5 to 7 minutes or until lightly toasted and fragrant. Cool completely in pan on a wire rack (about 15 minutes).
2. Stir together mayonnaise and next 4 ingredients in a large bowl. Fold in pecans, chicken, and peaches; cover and chill 2 hours. Garnish, if desired.