Cook the pasta in boiling salted water until slightly soft. It is a good idea to slightly undercook it as the pasta is going into the oven at a later time.
While the pasta is cooking fry the onion with the bacon in a large saucepan until the bacon is just cooked and the onion is soft.
Add the chicken and mix together. Add the herbs, salt and pepper then gradually stir in the tomato paste. When all has been mixed together gradually add the tinned tomatoes then bring to a simmer.
If the mixture feels too dry and sticky add a little water to loosen then add the Mascarpone along with a small handful of the grated cheddar. Mix until all the cheese and mascarpone has been blended in.
Drain the cooked pasta and rinse under a cold tap to remove any starch and then mix into the tomato chicken and bacon mixture until everything is coated and even.
Place the whole mixture into a large oven dish and sprinkle the remaining grated cheese on top so that it is evenly coated. Put this into the oven at about 140 degrees C until the dish is heated through and the cheese is golden and bubbling. Serve with garlic bread if desired.