In a medium bowl, whisk flour, baking powder, and salt. Set aside.
In a separate large bowl, cream the room temperature butter and granulated sugar. Beat the egg and vanilla extract into the butter and sugar mixture until smooth.
Gradually add the dry ingredients to the wet mixture, stirring until a dough forms. If the dough is too dry, add a splash of orange juice. Knead the dough.
On a floured surface, roll out one of the chilled dough disks to a 1/8-inch thickness. Use a 3-inch cookie cutter to cut out circles. Place the circles on the prepared baking sheet.
Place a strip of mozzarella cheese and a strip of guava paste in the center of each dough circle.
Fold the dough over the filling to create a triangle shape, ensuring the filling remains visible at the center. Pinch the corners to seal the edges.
Bake the pastries for 20-25 minutes until they turn lightly golden.