1. Cook pasta according to package directions and drain.
2. In a large skillet, simmer tomatoes, tomatoe sauce, oregano, salt, and 2 cloves garlic.
3. Brown onion, remaining garlic, mushrooms, and Italian sausage over medium heat.
4. In a 3 quart casserole dish, layer the following: 1/2 of the rigatoni, 1 cup cheese, sour cream, 1/2 of the sauce, remaining rigatoni, 1 cup cheese blend, and remaining sauce. Top with grated Parmesan cheese.
4. Bake at 350 degrees for 30 minutes, or until cheeses are melted.