In a large Dutch oven or soup pot with a tight-fitting lid, combine the vegetable broth, spaghetti, tomatoes, onion, garlic, basil and crushed red-pepper flakes. Bring the mixture to a boil over medium-high heat, then cover and reduce the heat to medium.
Cook, stirring frequently, until all the liquid has been absorbed and the pasta is fully cooked, 13 to 15 minutes. Season with salt and pepper.
Serve topped with Parmesan cheese.
