Heat the oven to 400 degrees F. Beat the egg and water in a small bowl with a fork or whisk. Stir the cheese and salsa in a small bowl.
Unfold the pastry sheet on a lightly floured surface. Roll the pastry sheet into a 15 x 12-inch rectangle. Cut into 20 (3-inch) squares. Place about 1 tablespoon cheese mixture in the center of each pastry square. Top each with 1 olive piece, if desired. Brush the edges of the pastry squares with the egg mixture. Fold the pastry over the filling to form triangles. Crimp the edges with a fork to seal. Place the filled pastries onto baking sheets. Brush the pastries with the egg mixture and sprinkle with the chili powder.
Bake for 15 minutes or until the pastries are golden brown. Remove the pastries from the baking sheets and let cool on wire racks for 10 minutes.
Pepperidge Farm® Puff Pastry