Put the lentils in a pan, cover with 500ml cold water, crumble in the stock cube, bring to the boil and boil for 5 minutes. Reduce the heat, cover and simmer for a further 20 minutes or until tender. Drain and reserve 100ml stock.
15 minutes before the lentils are ready, cook the linguine or spaghetti in boiling water for 9-11 minutes, or until just tender.
Heat the olive oil and butter in a frying pan and cook the onion for 4-5 minutes or until soft. Add the mushrooms and cook for another 4-5 minutes or until soft.
Add the cheese, stock, and parsley, and cook for a further 2-3 minutes.
Add the drained lentils and combine. Drain the pasta and stir into the sauce.