Dice the chicken breast and season it with salt and pepper, then set aside.
Peel and finely chop the onion and 4 garlic cloves. Brush the mushrooms and cut them in quarters.
Heat up a non-stick deep frying pan and coat it with 2 puffs of olive oil. Add the chicken and fry it until it changed color on all sides, should be done in 5-6 minutes.
In the mean time, boil the pasta according to the package instructions. Drain and set aside.
Take out the chicken to a bowl, then add the butter, the onion, garlic and mushrooms.Leave to saute with a lid on for about 10 minutes, stirring from time to time.If you see that there is not enough moisture in the pan, add 3-4 tbsp of hot water. Add the tomato puree and leave to boil for a minute.
Turn on the oven to preheat at 190°C.
Add the chicken breast to the pan (along with the juice it left in the bowl while sitting aside), the heavy cream and 1 tbsp grated parmesan, then bring to boil for 1 minute.Mince the remaining garlic clove and mix thoroughly. Lay the drained tagliatelle in a non-stick high wall oven tray and pour the obtained sauce on top of it. Give it a few stirs and top it with the remaining parmesan, grated mozzarella and freshly ground pepper. Cook in the oven for 7 minutes until the cheese is all melted.
Serve hot with additional grated parmesan and ground pepper to taste.