Heat oven to 375°F. On ungreased cookie sheet, place fillo shells. Microwave squash as directed on package.
Meanwhile, in 10-inch skillet, melt butter over medium heat. Cook onion in butter 3 to 4 minutes, stirring occasionally, until tender. In medium bowl, mix onion, squash, sage, salt and pepper until blended. Spoon mixture evenly into fillo shells.
Bake 8 to 10 minutes or until warm. Sprinkle with bacon.