Waldorf Chicken-Salad Sandwiches

In a 3-quart saucepan, combine chicken, onion, peppercorns, and 1/2 teaspoon salt with enough cold water to cover. Bring to a simmer over medium heat. Reduce heat to low, and simmer until chicken has cooked through, 15 to 18 minutes. Drain and set aside until chicken is cool enough to touch. Discard onion and peppercorns.

In a medium bowl, combine mayonnaise, olive oil, vinegar, mustard, tarragon, pepper, and the remaining 1/4 teaspoon salt.

Chop chicken into 1/2-inch pieces and toss with tarragon dressing. Toss with apple, celery, and pecans.

Slice baguettes lengthwise and place lettuce on bottom halves. Top with chicken salad, cover with baguette, and cut each baguette in half.