Add the pasta to a large pan of salted boiling water and cook for the recommended time. Add the runner beans for the last 6 mins of cooking time.
In the meantime saute the chopped bacon and mushrooms in the oil (and chopped leeks if using). When the pasta is almost done take off the heat and stir through the yoghurt to make the sauce.
Darin the pasta and veg, reserve a cup of the pasta water.
Add the pasta and veg to the mushroom mix, loosen with a little of the pasta water if needed.
Serve and sprinkle with parmesan and chopped parsley if you have some.