In a large pot of boiling, salted water, cook the pasta until al dente, about 8 minutes; drain and rinse with cold water.
Meanwhile, in a large skillet, heat the olive oil over medium heat. Add the onion and cook until softened, about 5 minutes. Add the beef and cook, breaking up the meat, until browned, about 5 minutes. Stir in 2 cups tomato sauce, the brown sugar and Worcestershire sauce and simmer for 5 minutes. Let cool slightly.
Drizzle a 9-by-13-inch casserole with 1/4 cup of the remaining tomato sauce. Stuff each manicotti with 1/4 cup of the meat mixture and place them side by side in the casserole. Spoon the remaining tomato sauce over the manicotti and top with the cheese. Bake until golden and bubbly, about 15 minutes.