Chicken Salad Sandwich

I saw this on "The Barefoot Contessa" and modified it to make it even lighter. It is a tangier and quicker version of the regular chicken salad. Oh, and Misty keeps bugging me to put it on here...just for you Mist!Chicken Salad
2-3 c. chopped chicken (I use a rotisserie chicken, chilled and chopped)
1 c. chopped celery
1 c. cherry tomatoes, halved
1 c. mayo and plain yogurt (I mix them to make it lighter, using more yogurt)
1/4 c. dijon mustard
1/8 c. whole grain mustard
1/2 t. salt (or to taste)
1/4 t. pepper (or to taste)
1 T. chopped fresh tarragon

Add chicken, celery, tomatoes, and tarragon to a large bowl. Mix together remaining ingredients in a small bowl and whip until smooth. Add as needed to chicken and toss. Chill for 2 hours to overnight. Serve on sandwich rolls or croissants.