THAW pastry sheets at room temperature for 40 min. Preheat oven to 400°F. Lightly grease 2 large baking sheets. Set aside.
UNFOLD 1 pastry sheet on lightly floured surface. Roll out to a 12"x12" square. Cut into 36 (2") squares. Prick pastry squares several times with fork. Place on prepared sheets. Repeat with remaining pastry sheet.
BAKE for 8 min. or until slightly puffed and golden.
PRESS down puffed centers of pastry squares if necessary. Top each pastry with about 1 tsp. each cheese and bacon.
BAKE for 5 min. more or until cheese is melted and lightly browned. Garnish with dressing and chives. Serve warm.