Preheat oven to 425F.
In a large bowl, mix together beef, egg, parmesan cheese, bread crumbs, Worcestershire sauce, salt, pepper, and red pepper flakes until the ingredients are well combined. Form mixture into 1½-inch meatballs and place on foil-lined baking sheet. Bake for 10 minutes until the meatballs are set (may not be completely cooked through).
Meanwhile, cook spaghetti in a large pot of salted water until al dente. Drain and reserve a cup of pasta water for later use.
In a large pot, sauté garlic and onion in olive oil until soft, 5 to 7 minutes. Add marinara sauce, herbs, and sugar, and bring to a boil. Add meatballs to the pot and simmer on low for 15 minutes. Season sauce with salt and pepper to taste. Toss cooked pasta with the sauce, adding pasta water to thin out if necessary. Serve with cheese and bread, if desired.