Heat the olive oil in a 5-6 quart Dutch oven over medium heat.
Add the sliced onion and garlic and sauté for 2-3 minutes until fragrant and translucent.
Add the dry spaghetti, diced tomatoes with juice, vegetable broth, dried oregano, dried basil, red pepper flakes, salt, and black pepper to the Dutch oven.
Stir everything together to combine and ensure the pasta is submerged in the liquid.
Bring the mixture to a boil over high heat.
Once boiling, reduce heat to medium-low and simmer uncovered, stirring occasionally, until the pasta is cooked al dente and most of the liquid is absorbed, about 10-12 minutes.
Remove the Dutch oven from heat and stir in the grated Parmesan cheese until melted and well combined.
Sprinkle chopped fresh parsley over the pasta before serving.