Heat oven to 350°F. Spray 3-quart casserole with cooking spray. In 3-quart saucepan, cook and drain pasta as directed on package using minimum cook time. Return pasta to saucepan.
While pasta is cooking, cook sausage and onion in 10-inch skillet over medium heat 6 to 8 minutes, stirring occasionally, until sausage is no longer pink; drain. Stir sausage mixture, bell pepper, water, bacon, pizza sauce and mushrooms into pasta. Spoon pasta mixture into casserole. Sprinkle with cheese.
Cover casserole. Bake 30 to 35 minutes or until hot and cheese is melted.