Mix the water, the mayonnaise and the yoghurt together in a pan and bring to a gentle boil then remove from the heat. Place the pasta in an oven-proof dish and sprinkle the chopped bacon (or ham) over the top. Pour on the sauce mixture and top with grated cheese
Bake in a preheated moderate oven (Mk 4 - 350ºF - 180ºC) for 30 minutes and serve hot with a salad or your favourite vegetables.