In a medium mixing bowl, combine fat-free Greek yogurt and mayonnaise. Add distilled white vinegar, kosher salt, and fresh ground black pepper. Whisk until smooth.

Gently fold diced shallots and cooked shredded rotisserie chicken into the dressing until evenly coated.

Cover and refrigerate the chicken salad mixture for at least 1 hour to enhance flavors.

Take two slices of multigrain bread, spread the chicken salad mixture over one slice, add lettuce, and top with the second slice.

Cut the sandwich in half diagonally and serve.