Preheat the oven to 200°C/400°F/gas mark 6. Place the soaked chestnuts, herbs and 170 ml of the wine in a saucepan with just enough vegetable stock to cover and cook until just tender (about one hour). Drain the chestnuts, keeping the liquid.
Meanwhile, cook the lentils in a separate pan with water. (Bring to the boil then simmer for about 45 minutes.)
Melt the margarine in a frying pan and sauté the onions on a low heat until slightly browned. Add the mushrooms and cook for a further five minutes.
Add the chestnuts, lentils, the remaining red wine and sufficient chestnut cooking liquor to cover. Bring to the boil and simmer for about 20 minutes to reduce the liquid a little.
Stir in the mustard, soy sauce and black pepper to taste. Cook for a further five minutes. Check the seasoning and adjust as necessary.
Spoon the mixture into a pie dish. Roll out the pastry on a floured surface and place on top of the filling. Bake for about 20 minutes until a golden crust forms.