Bring a pot of salted water to boil for the pasta. As soon as it is boiling, add the pasta and cook according to the package directions. Don't overcook the pasta.
Heat olive oil in a saute pan and add garlic and cook about 1 minute then add the chopped onions and Italian seasoning and red pepper flakes. Break the sausage meat apart and add to pan and stir to cook; about 5 minutes. Add the mushrooms and continue to cook; about another 5 minutes. Add the spinach and cook until wilted. Stir in cream and the Parmesan cheese.
Place the pasta in a serving bowl; top with the sauce and toss gently to combine. Pass additional Parmesan cheese if desired.