Cook pasta according to the packet instructions until al-dente. Then drain.
Whilst pasta is cooking gently heat the olive oil in a large saucepan and add the bacon. Lightly fry the bacon until it is just beginning to crisp then remove it from the saucepan with a slotted spoon and set aside.
Sauté the onion in the same oil until softened (add a little water to the pan if oil has evaporated) then add the milk and cornflour mixture. Keep stirring until the sauce has thickened and then season to taste.
Add back the cooked bacon and stir in the green beans. Allow to simmer for a minute, add the cooked, drained pasta and combine everything well.
Remove the mixture to a casserole dish, spread out evenly and sprinkle the cheese over the top.
Bake in the centre of an oven for approximately 15 minutes until the cheese has browned slightly and is bubbling.
Serve with a crispy salad.
*I use turkey bacon because it is healthier, but you could use other types of bacon.