Cook the Pasta:Bring a large pot of salted water to a boil. Cook the spaghetti according to package directions until al dente. Drain and set aside.
Brown the Beef:In a large skillet or saucepan, heat olive oil over medium heat. Add chopped onions and cook for 3-4 minutes until translucent. Add garlic and sauté for another minute.
Add the Meat:Add ground beef to the skillet. Break it up with a spoon and cook until browned and no longer pink. Drain excess fat if needed.
Build the Sauce:Stir in the crushed tomatoes, tomato sauce, and tomato paste. Mix well. Add oregano, basil, salt, pepper, sugar (if using), and red pepper flakes.
Simmer:Reduce heat to low. Cover and let the sauce simmer for 15-20 minutes, stirring occasionally to blend the flavors.
Combine:Toss the cooked spaghetti with the meat sauce or serve the sauce on top of the noodles.
Garnish and Serve:Sprinkle with Parmesan cheese and fresh parsley. Serve hot and enjoy!