Preheat oven to 204 °C (200 °C). Line a baking sheet with parchment paper.

Gently unfold the puff pastry sheet onto the prepared baking sheet. Score a 1-inch border around the edges with a sharp knife, being careful not to cut all the way through. Prick the center of the pastry all over with a fork.

In a small bowl, combine ricotta cheese, chopped dill, chives, lemon zest, salt, and pepper. Mix well.

Spread the herbed ricotta mixture evenly within the scored border of the puff pastry.

Arrange the prosciutto slices over the ricotta, tearing them into smaller pieces if necessary.

Scatter the asparagus spears and peas evenly over the prosciutto.

In a small bowl, whisk together the egg and water to create an egg wash. Brush the scored border of the puff pastry with the egg wash.

Bake for 20-25 minutes, or until the puff pastry is golden brown and puffed, and the vegetables are tender-crisp.

Remove from oven, sprinkle with grated Parmesan cheese, and let cool slightly before slicing and serving.