Boil pasta according to the package directions
Meanwhile, cook the Italian sausage with the onion in a large pan over med/high heat
Add minced garlic and cook another minute
Add the mushrooms and sauce
Bring to a boil and cook for a few minutes longer
In a small bowl, mix the egg, cottage cheese, spinach, and parmesan cheese
When the noodles have cooked - drain them
In a 9x13 pan, add a few ladles full of pasta sauce
On top of the sauce, add the noodles
Then over that, spoon the egg/cheese mixture - spread out
Spoon out the rest of the pasta sauce and spread it out
Top with mozzarella cheese
Cover with non-stick foil
Bake for 45 minutes at 375 degrees
Uncover and bake for another 15 minutes