Heat the oven to 350°F and grease a 9-by-13-inch baking dish.
Boil the macaroni for 2 minutes less than the package directs, then drain it well.
Brown the beef, sausage and onion in a large skillet over medium-high heat for 8 to 10 minutes, until the meat reaches 160°F, then drain the fat.
Add the mushrooms and cook for 5 minutes, until they soften and their liquid evaporates.
Stir in the crushed tomatoes, tomato sauce, oregano, salt and pepper and simmer uncovered for 10 minutes, until thickened.
Fold in the macaroni and 1 cup cheddar, spread the mixture in the dish and cover with the remaining cheddar.
Bake for 25 to 30 minutes, until bubbling in the center and browned around the edges, then rest for 10 minutes.