Place cookie sheet on oven rack. Heat oven to 400°F.
Meanwhile, in 10-inch nonstick skillet, cook sausage, mushrooms and onion over medium-high heat 5 to 7 minutes, stirring frequently, until sausage is no longer pink; drain. Stir in sweet potato and water; heat to boiling. Reduce heat; cover and simmer 6 to 7 minutes or until vegetables are tender. Uncover; cook 2 to 3 minutes longer or until liquid is evaporated. Remove from heat; stir in 1/2 cup of the cheese. Spoon into partially baked crust.
Bake on cookie sheet 25 minutes, covering loosely with foil last 10 minutes of baking. Sprinkle with remaining cheese. Bake uncovered about 5 minutes longer or until cheese is melted. Let stand 5 minutes before serving.