Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente, about 9-11 minutes. Drain and set aside.
While the pasta cooks, heat olive oil in a large skillet over medium heat.
Add the chopped onion and sauté for 3-4 minutes until translucent.
Add the minced garlic and cook for 1 minute until fragrant.
Add the ground beef to the skillet. Cook, breaking it up with a spoon, until browned and cooked through, about 6-8 minutes. Drain excess fat if necessary.
Stir in the crushed tomatoes, tomato paste, dried oregano, dried basil, salt, black pepper, red pepper flakes, and beef broth.
Bring the sauce to a simmer and cook for 15 minutes, stirring occasionally, until slightly thickened.
Add the cooked spaghetti to the skillet with the sauce and toss to combine evenly.
Divide the pasta and beef sauce among four plates.
Sprinkle each serving with grated Parmesan cheese and chopped fresh parsley before serving.