Heat oven to 177°C. Heat large nonstick skillet over medium heat until hot. Add Ground Beef and yellow onion; cook 8 to 10 minutes, breaking into 2cm crumbles and stirring occasionally. Pour off drippings. Stir in sloppy Joe sauce, rotini and water.
Spray 33 x 23 cm glass baking dish with cooking spray. Spoon beef mixture into dish; cover with aluminum foil. Bake in 177°C oven 35 to 40 minutes or until pasta is tender. Uncover; sprinkle with cheese. Continue baking, uncovered, 5 minutes or until cheese is melted.
Let stand 5 minutes before serving. Garnish with green onions, if desired.