Heat olive oil in a large pot over medium heat. Add the sausage, breaking it up into bite sized pieces. Cook until lightly browned, about 8-10 minutes.
Add the onions, cook until tender, about 5-7 minutes.
Add the garlic, oregano and red pepper flakes, sauté until fragrant, about 1 minute. Add tomato paste and stir well to incorporate. Cook for 3 to 4 minutes, or until the tomato paste turns a rusty brown color.
Add diced tomatoes, bay leaves, and chicken stock. Stir to combine. Bring to a boil and then reduce heat and simmer for 30 minutes.
Add the pasta and cook until al dente, about 7 minutes and remove from heat. Season with salt and pepper, to taste.
While the pasta is cooking, prepare the cheese filling. In a small bowl, combine the ricotta, Parmigiano-Reggiano cheese, salt, and pepper, set aside.
To serve, place a dollop of the cheese filling into individual soup bowls, top with a ladle the hot soup, sprinkle with mozzarella cheese and garnish with fresh chopped basil.