Preheat the oven to 200°C and line a baking tray with baking paper. Whisk the egg yolk in a small bowl and set aside.
Using a clean tea towel or paper towel, squeeze excess moisture from the grated carrot and zucchini.
Add the chicken mince, grated vegetables, diced onion, garlic, ketchup, salt, and black pepper to a large mixing bowl. Mix well until fully combined.
Lay the puff pastry onto a lightly floured surface, or baking paper, and cut each 300g pastry sheet into 6 rectangles.
Spoon the chicken mixture onto each pastry. Brush the opposite edge lightly with egg wash.
Roll the pastry tightly around the filling, finishing seam-side down. Repeat with the remaining pastry and filling mixture.
Brush the tops with egg wash and sprinkle with sesame seeds if using.
Bake for 25–30 minutes, or until golden brown and cooked through.
Allow to cool for 5–10 minutes before serving.