Unfold puff pastry; cut into 25 squares. Transfer to greased baking sheets. Bake at 400° for 11-13 minutes or until golden brown.
Meanwhile, grate one shallot and finely chop the other. In a small bowl, combine the shallots, mustard, mayonnaise and vinegar. While whisking, gradually add oil in a steady stream. Spoon a small amount of sauce onto each pastry; layer with arugula and salmon. Drizzle with remaining sauce and sprinkle with cheese. Yield: 25 appetizers.