Heat oven to 375°F. In 12-inch nonstick skillet, cook beef and onion over medium-high heat, stirring frequently, until beef is browned and thoroughly cooked; drain. Add tomato pasta sauce and water; mix well. Heat to boiling. Add noodles; return to boiling. Reduce heat to medium; cover and cook 12 to 15 minutes, stirring occasionally, until noodles are tender.