Pre-heat the oven to 180ºC. Spray the loaf tin with low calorie cooking spray and line with baking parchment.
Spray a large frying pan with low calorie cooking spray and sauté the onions, carrots and mushrooms over a medium heat for around 10 minutes. The vegetables will release some liquid. Keep sautéing until this has evaporated and you have a drier mix.
Add the garlic granules, thyme and soy sauce, and stir over the heat for another minute.
Stir in the tomato puree and white wine vinegar.
Place the cooked vegetables in a mixing bowl, along with the breadcrumbs and chestnuts and mix until well combined.
Taste the mix and add some salt and pepper according to taste.
When you are happy with the seasoning, stir in the egg, and press the mix into the prepared loaf tin.
Bake in the oven for 30-35 minutes, until golden and firm to touch.
Allow to rest in the tin for 10 minutes, before turning out and cutting into 6 slices.
Serve with traditional Christmas accompaniments.