Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

In a food processor, combine walnuts, a pinch of salt, and peeled garlic cloves. Pulse until chunky, then add basil and lemon juice, pulsing to combine. Slowly drizzle in olive oil until smooth, then fold in Parmesan cheese.

On a floured surface, roll out the thawed puff pastry. Slice into 9 equal squares, approximately 4x4 inches.

Place a generous dollop of pesto in the center of each pastry square, followed by a slice of tomato and mozzarella. Fold opposite corners together and pinch to seal.

Chill the assembled pastries in the refrigerator for about 20 minutes.

Brush each pastry with an egg wash made from a beaten egg and sprinkle with garlic salt and Parmesan. Bake for 20-25 minutes until golden brown.

Cool slightly, drizzle with balsamic glaze, and garnish with basil leaves before serving.