In small bowl, combine first 5 ingredients; spoon into piping bag with star tip or qt.-sized zipper-closure food storage bag. Cut 1/2" opening in one of the bottom corners of storage bag; set aside. Cut a small slice off top of each tomato. Using a melon baller or small spoon, scoop out inside of each tomato. Pipe filling into cavity of each tomato.
To Serve: Line dinner-sized plate with shredded lettuce; arrange tomatoes among lettuce. Refrigerate at least 1 hr., covered.