Combine first 5 ingredients in a large saucepan; add water to cover. Bring to a boil; cover, reduce heat, and simmer 30 minutes or until chicken is tender. Drain; remove chicken, and cool. Discard liquid.
Remove meat from bones; coarsely chop chicken. Combine chicken, grapes, and pecans in a bowl. Stir mayonnaise, mustard, and seasoning into chicken mixture. Cover and chill.
Place lettuce on each of 4 bread slices; top each with 3/4 cup chicken salad and remaining bread slice.