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