In a small bowl, stir together mascarpone cheese, basil, tomatoes, salt, and garlic powder until combined.
Spread 1 tablespoon cheese mixture onto a bread slice. Top with 2 turkey slices and another bread slice. Spread 1 tablespoon cheese mixture onto bread slice. Top with 2 turkey slices and another bread slice to create a triple-stack sandwich. Repeat with remaining bread, cheese mixture, and turkey to make a total of 4 sandwiches.
Using a serrated bread knife in a gentle sawing motion, trim and discard crusts from each sandwich to make 4-inch squares. Cut each into 4 (2-inch) squares.
To garnish, tie each tea sandwich with 2 chives to look like presents, if desired. Serve immediately, or cover with a damp paper towel, place in an airtight container, and refrigerate until serving time.
Notes
Blanch fresh chives in hot water until pliable, approximately 5 seconds. Blot dry with paper towels. Tie chives around tea sandwiches.
Recipe by TeaTime Magazine at https://teatimemagazine.com/turkey-pesto-tea-sandwiches/