Herbed Chicken Salad Sandwiches

1 Tbs. finely chopped fresh tarragon
3 Tbs. mayonnaise
3 Tbs. plain Greek yogurt
1 Tbs. fresh lemon juice
1/8 tsp. kosher salt
2 cups chopped skinless, boneless rotisserie chicken breast
1/4 cup minced sweet onion
8 slices gluten free rye style sandwich bread
4 leaf lettuce leaves
Combine the first 5 ingredients in a large bowl. Stir in chicken and onion. Top 4 bread slices with 1 lettuce leaf and about 1/2 packed cup chicken salad. Cover with additional slice of bread and serve. (Yield 4 servings)