Very easy. First check that the stock isn't too salty though - it can be awful sometimes and spoil the soup.
Leave the stock in the pan when you take the meat out, add red lentils, chopped onions, carrots, acorn squash, and a few chillies (not essential obviously). Let the whole lot simmer for an hour or so. Then blend. I can't give you quantities I'm afraid as I'm a 'chuck it all in' sort of cook.