Brown beef and onion in a Dutch oven, breaking the meat into very fine crumbles; drain excess fat.
Add garlic and tomato paste and cook for 1 minute.
Stir in crushed tomatoes, tomato sauce, brown sugar, oregano, salt and pepper and simmer uncovered for 20 minutes.
Boil broken spaghetti in salted water until tender and drain, reserving 1 cup pasta water.
Fold spaghetti and Parmesan into the sauce, adding enough pasta water to keep it loose and scoopable.
Simmer together for 2 minutes and serve in shallow bowls.