Line unpricked pastry shell with a double thickness of heavy-duty foil. Bake at 450° for 8 minutes. Remove foil; bake 5 minutes longer. Cool on a wire rack. Reduce heat to 350°.
In a large skillet, cook sausage and onion over medium heat until meat is no longer pink; drain. Transfer to a large bowl. Stir in the eggs, cheddar cheese, milk, oregano and pepper. Pour into crust.
Bake for 30-35 minutes or until a knife inserted in the center comes out clean. Spread pizza sauce over sausage mixture; top with cheese. Bake 5-8 minutes longer or until cheese is melted. Let stand for 10 minutes before cutting.