Heat the oil in a Dutch oven or large pot over medium-high heat. Add the sausage and cook, breaking up into pieces, until browned, about 5 minutes. Add the onions and cook until completely softened, about 5 minutes. Add the garlic, oregano, and red pepper flakes and cook until fragrant, 30 second to 1 minute. Add the tomato paste and stir until incorporated. Continue cooking for another 3 to 4 minutes, or until the tomato paste begins to turn a rusty brown color. Add in the diced tomatoes, chicken stock, and bay leaf. Bring to a boil then reduce heat and simmer for 30 minutes.
Add the uncooked pasta and cook in soup until al dente.
Meanwhile, combine the ricotta, Parmesan, and mozzarella in a small bowl. Season to taste with salt and pepper.
Once the pasta is cooked season the soup to taste with salt and pepper then immediately divide the soup between four bowls. Divide cheese mixture among bowls. Garnish with fresh basil.