Heat oven to 400˚F. Using 1¾” diameter round cookie cutters, cut 4 circles in each puff pastry round (you will have 48 rounds). Divide cut pastry rounds evenly among baking trays fitted with parchment paper, leaving 1” spaces between each round.
Bake until light golden brown and puffed, about 8 minutes. Using back of small spoon or melon baller, press down centers of hot pastries to make indentation.
Place one piece each queso blanco and guava paste into each indentation. Bake until guava and cheese are soft and melted, about 8 minutes.
Transfer pastries to cooling rack. Press walnut piece into each pastry. Let pastries sit until cool, about 10 minutes.