Using a 1¾-inch square cutter, cut 42 squares from frozen bread slices. To let thaw and to prevent bread from drying out during assembly, cover with damp paper towels, or store in a resealable plastic bag.
In a large bowl, combine chicken, mayonnaise, sour cream, basil, lemon zest, salt, and pepper, stirring to blend. Add almonds, stirring until combined.
Spread half of chicken salad in a thin layer onto 14 bread squares. Top each with another bread square, and spread with a thin layer of remaining chicken salad. Top each with a third bread square to make 14 triple-stack sandwiches. Serve immediately, or cover with damp paper towels, place in a covered container, and refrigerate until serving time.
Recipe by TeaTime Magazine at https://teatimemagazine.com/lemon-basil-chicken-salad-sandwiches/