Steps
1. Preheat the oven to 200°C (390°F).
2. Heat olive oil in a pan over medium heat.
3. Sauté the onion, zucchini, and bell pepper until tender (about 5-7 minutes).
4. Season the vegetables with salt and pepper, then let cool slightly.
5. Roll out the puff pastry sheet on a lightly floured surface.
6. Cut the pastry into two equal squares.
7. Place the vegetable mixture in the center of one square, then sprinkle the grated cheese on top.
8. Brush the edges of the pastry with beaten egg.
9. Cover with the second pastry square and press edges firmly to seal.
10. Brush the top with the remaining egg wash for a golden crust.
11. Place the pastry on a baking tray lined with parchment paper.
12. Bake for 20-25 minutes until the pastry is puffed and golden brown.
13. Let cool for a few minutes before serving.