Boil the spaghetti following the instructions on the packet.
Gently fry the leek over a low heat in a frying pan with a dash of extra-virgin olive oil. When it has turned golden brown, add the sliced carrot. After a few minutes, add the zucchini and mushrooms and continue gently frying until all the vegetables are cooked al dente. Add salt and pepper to taste.
To make the sauce, leave the cashew nuts to soak for a few hours. Once they are soft, strain and blend them with the lemon juice, walnut drink and yeast (you can thin out the sauce by adding more walnut drink). Add a pinch of salt.
Pour the sauce into the frying pan with the vegetables. Add the cooked spaghetti, turn off the heat and stir well. Add more salt to taste.