Preheat oven to 375 degrees F.
Place chicken on a parchment-lined baking pan, drizzle with olive oil and season with salt and pepper.
Bake for 35 minutes, or until internal temperature registers 165 degrees F on a meat thermometer.
Once chicken has cooled, remove skin and meat from bones and chop into chunks (you should have about 3 cups).
In a large bowl, combine mayonnaise, yogurt, lemon juice, mustard and tarragon.
Add chicken, celery and pecans to dressing ingredients. Combine well and season with salt and pepper to taste.