Put water in a big pot and add some salt (if you want). Bring it to boil and then put the pasta in it. Leave it for some minutes till it gets ready (as instructed on the packet). Never overcook pasta.
While the water boils, peel the sausage to remove its skin. Cut the sausage into thin slices. Fry the sausage till it gets a golden brown-color. I do not fry the sausage, but I put it into the microwave. I put it into a small bowl and cover it before microwave it for ~3min. When it is ready, take the sausage out into a plate and through away the fat in the bowl.
In another (smaller) pot put the tomato puree. Add the olive oil, some black pepper and/or the chili paste. Leave the mixture to simmer at low heat.
While waiting for the pasta to boil, put the mozzarella into the tomato sauce and stir till it starts melting nicely. The sauce shall get a pinkish color instead of the intense red it had at the beginning.
When the pasta is almost ready, put in the sauce pot the sausage, stir a bit and turn off the heating.
When the pasta is ready, drain it (and if you want wash it under cold water).
Put the pasta into the plates and pour the sauce on top of it.
Add the parmesan cheese on top of it and serve. Parmesan cheese is not necessary for this recipe as the sauce already has cheese in it (mozzarella)
And as Julia Child would say: "Bon Appetite!"