Preheat oven to 350°F.
Combine spinach, cheeses, and tarragon. Add salt and pepper, if desired.
Lift up skin of each chicken breast and divide mixture evenly among them. Be careful not to tear skin. Smooth skin over stuffing; tuck underneath to form a neat package.
Brush each breast with melted margarine. Place in 2-quart baking dish.
Bake uncovered for 45–50 minutes until chicken is browned and no trace of pink remains.
Remove and discard skin after cooking.
This recipe excerpted from The Complete Month of Meals Collection. ©2017 by the American Diabetes Association. Available at ShopDiabetes.org.