Preheat the oven to 200°C fan (220°C conventional).
Grate the potato, carrot and zucchini, then wrap in a clean tea towel and squeeze out as much liquid as possible. This is the key to avoiding soggy sausage rolls.
Mix the chicken mince, potato, zucchini, carrot, celery, spinach, breadcrumbs, egg, mustard, herbs, spices, parsley and seasonings until just combined.
Divide the mixture into four even portions and shape into logs.Cut each pastry sheet in half.
Place a log along one long edge, brush the opposite edge with egg wash, roll up tightly and seal.
Cut each log into three pieces, brush with egg wash and bake for 30–35 minutes, until the pastry is crisp and golden and the filling reaches 75°C.