Bring a pot of water to a boil. Prick the sausage casing with a fork and add to the pot. Boil for about 2-3 minutes, (casing should be pale). This will allow some of the fat from the sausage to boil out.
Remove the sausage from the water. Once cool enough to handle, remove the casing, then chop the sausage.
Add the sausage to deep skillet or pan and cook for about 5 minutes over medium heat.
Add onion and garlic and cook until softened and translucent.
Drop in the mushrooms and cook until tender, reduce heat to medium low.
Add tomato sauce and basil, mix and reduce heat to low.
Preheat oven to 350 degrees.
Cook pasta according to package directions. Once done, drain the pasta.
Place about 1/3 of the sauce in the bottom of the baking dish, making sure to cover the bottom.
Top with 1/2 of the pasta, spreading evenly.
Add another 1/3 of the sauce, then the rest of the pasta.
Cover the top with remaining sauce and sprinkle shredded mozzarella cheese on top.
Bake for 25-30 minutes or until cheese is melted and just browning, sauce should be bubbling.
Remove from oven, serve and enjoy!
Store leftovers in the refrigerator for up to 3 days.
To freeze: layer sauce and pasta and let casserole cool completely. Top with cheese. Cover with heavy duty foil and freeze for up to three months. Take casserole out a night before use and place in the refrigerator to thaw. Bake at 350 degrees until the sauce is bubbling and cheese is melted and just starting to brown.