To rehydrate the porcini mushrooms, place in a bowl and cover with boiling water. Allow to soften for 15 minutes.
Finely chop the onion, carrot and garlic cloves. In a large casserole dish, heat the oil over a low heat. Add the onion and carrot and sweat for 8-10 minutes until softened and translucent.
Add the chopped garlic, rosemary, oregano and tomato paste and sauté for a minute.
Meanwhile, drain the porcini mushrooms and slice into thin pieces. Add the porcini and chestnut mushrooms to the pan and stir through for a further minute.
Now increase the heat to moderate-high and pour in the wine. Allow to reduce over 2-3 minutes.
Next pour 2 tins of 400g plum tomatoes into a separate bowl and use a pair of scissors to chop into small chunks. Add these to the dish along with the lentils, vegetable stock, salt and sugar.
Reduce heat to low and cover. Simmer for 1 hour, checking periodically to add water if the sauce starts to look dry.
In the final 10 minutes begin to cook the spaghetti. Add the pasta to a pan of well salted boiling water. Cook until al dente, approximately 8-10 minutes. Drain well and allow to steam dry for a minute before dividing up onto plates.
Taste the bolognese to ensure the lentils are cooked through; they should have a slight bite to them. Season with salt and pepper as required. Spoon the lentil bolognese onto the pasta. Serve alongside a crisp dressed salad and crunchy fresh bread.