1. Heat oven to 375 Degrees F. Coat baking sheet with nonstick cooking spray.
2. Beat cream cheese, sweetened condensed milk, lemon juice and cornstarch in medium bowl with electric mixer on medium speed for 1 minute or until smooth.
3. Roll pastry on floured surface with rolling pin into 12 x 9-inch rectangle. Cut in half crosswise, making two 9 x 6-inch rectangles. Place one half on prepared baking sheet. Stir guava paste until smooth. Spread onto pastry to within an inch of edge. Spoon cream cheese mixture evenly over guava paste.
4. Brush edges of pastry with beaten egg. Top with second half of pastry. Press edges with fork to seal. Cut six 4-inch diagonal slits in top of pastry. Brush top with beaten egg.
5. Bake 30 to 35 minutes or until puffed and golden. Cool on baking sheet 10 minutes. Transfer to wire rack. Cool completely. Cut into 6 bars.