In a large pot or Dutch oven, heat a splash of olive oil over medium heat. Add the Italian sausage, breaking it up with a spoon as it cooks. Cook for 5-7 minutes, or until the sausage is browned and cooked through.

Sauté the vegetables: Add the diced onion, bell pepper, and sliced mushrooms to the pot with the sausage. Cook for another 3-4 minutes, until the vegetables soften.

Add garlic and seasonings: Stir in the minced garlic, red pepper flakes (if using), and oregano. Cook for 1 minute until fragrant.

Add pasta and broth: Stir in the tomato paste, followed by the uncooked pasta and chicken broth. Bring the mixture to a simmer. Once simmering, reduce the heat to medium-low, cover the pot, and cook for 10-12 minutes, or until the pasta is tender and most of the liquid has been absorbed.

Add cheese: Once the pasta is cooked, stir in the shredded mozzarella cheese. Cook for an additional 2-3 minutes, until the cheese is melted and everything is well combined.

Serve and garnish: Serve the pizza pasta in bowls, and top with grated Parmesan cheese if desired. Enjoy!