Remove the puff pastry from the freezer about 45 minutes before using.
Preheat oven to 375℉ (190℃).
Line a baking or cookie sheet with parchment paper and set aside.
Whisk the cream cheese, powdered sugar, vanilla extract, and lime zest together by hand until smooth and well combined. Set aside.
Unroll the puff pastry, and cut each sheet into six 3"x 4" pieces (a total of 12 pastries).
Divide the guava paste into 12 portions and place a portion in the center of each pastry. Add about 1½ tablespoons of the cream cheese filling next to it, leaving some room around the edges.
Fold over, pressing gently to seal them with your fingers. Or seal them by pressing the edges with the tines of a fork.
Place the pastries on a baking sheet (or freeze them for later). Brush them with the beaten egg and sprinkle them with the caster sugar if desired.
Bake at 375℉ (190℃) for 18-22 minutes or until a beautiful golden brown.