Heat the oil in a large Dutch oven or soup pot over medium heat. Add the sausage (I took mine out of the casing) and brown for 5 minutes. I break mine up as I am cooking it, I do not want big chunks of sausage in my soup.
Add the onions and cook until soft.
Add the garlic, oregano, and red pepper flakes.
Add the tomato paste.
Let the tomato paste cook for a few minutes.
Add the tomatoes, bay leaves and chicken stock.
Bring the soup to a boil, and then turn down to a simmer. Simmer for 30 minutes. At the end, season with salt and pepper and add the basil.
While the soup is simmering, make the cheese mixture. In a small bowl, mix together the ricotta cheese, Parmesan, salt, pepper, and basil. Set aside.
When you are ready to serve your soup, add a good handful of pasta to the bottom of the bowl.
Add the soup to the bowl and add a generous spoonful of the cheese mixture to the top. Sprinkle with mozzarella cheese.