Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente, about 8-10 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 4-5 minutes until softened and translucent.
Add the minced garlic and cook for 1 minute until fragrant, stirring frequently to avoid burning.
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, water, and sugar.
Bring the sauce to a simmer. Reduce heat to low and cook uncovered for 15 minutes, stirring occasionally, until the sauce thickens.
Taste and adjust seasoning if needed.
Divide the cooked spaghetti among four plates. Spoon the meat sauce evenly over the pasta.
Sprinkle each serving with grated Parmesan cheese and chopped fresh parsley.
Serve immediately.