Tarragon adds a fresh flair to this Southern favorite. If desired, prepare the chicken salad two days ahead, and then assemble the sandwiches the morning of the party.
Stir together mayonnaise and next 4 ingredients in a large bowl. Add chicken, grapes, and chopped pecans, tossing to coat. Cover and chill at least 30 minutes.
Cut a slit horizontally on 1 side of each croissant; fill evenly with lettuce and chicken salad. Skewer sandwiches with fresh tarragon sprigs to hold together.