Preheat the oven to 200°C/fan 180°C/gas mark 6.
Boil the sweet potato in a pan of boiling water until soft, then drain.
Add ProZero and butter to the sweet potato and mash until smooth.
Heat the vegetable oil in a large saucepan over a medium-high heat.
Add butternut squash, onions, carrots, mushrooms, celery, parsnips, garlic, Worcestershire sauce, mixed herbs and tomato puree and cook for 5 minutes, until the vegetables start to brown.
Stir in the tinned tomatoes and vegetable stock.
Let the mixture simmer until sauce has reduced.
Divide the mixture into the 2 oven proof dishes.
Top with the sweet potato mash and bake in oven for 40 minutes, until golden brown.
ProZero is a food for special medical purposes and must only be used under medical supervision.