Pre-heat over to 180C fan.
Place potatoes and cauliflower together in a suitable sized saucepan and cover with cold water. Being them to the boil, then turn down allowing them to simmer for roughly 15 minutes until they are tender. Drain and set aside.
Whilst the potatoes and cauliflower are cooking, spray the bottom of a medium sized saucepan with the low calorie spray about 6 times. Turn the heat on high, then when the oil starts to bubble, turn down to a medium heat.
Add the onions and sauté for about 3 – 4 minutes, until soft, stirring constantly so they don't burn.
Add the Quorn mince, peas and carrots and combine together with the onions, then add the stock. Bring to the boil and allow to simmer gently for about 5 minutes.
Place the Quorn mixture into an oven proof casserole dish.
Mash the potatoes and cauliflower together and season to taste.
Spoon the potatoes and cauliflower mash over the top of the Quorn mince mixture.
Place into the oven on the centre shelf and bake for approximately 20 to 25 minutes until the topping is lightly browned.