Preheat oven to 450 degrees. Tear off 4 lengths of aluminum foil. Place chicken in center of lower half of foil, season chicken. Top with asparagus, carrot and onion.
In bowl combine butter, lemon juice and tarragon. Pour over chicken. Fold foil over chicken making folds with enough room for air expansion. Place foil packets on a baking sheet in a single layer. Cook 18-20 minutes.