Cook spaghetti according to the package directions, then drain and return back to the pot.
While your pasta is cooking, heat olive oil in a large skillet, add thinly sliced mushrooms, and cook them for about 10 minutes, stirring occasionally.
When the mushrooms are ready, add chopped onion, minced garlic, beef, salt, and pepper and cook for another 10 minutes until onions are soft and beef is no longer pink.
Add the tomato soup/sauce and bring to a boil.
Reduce the heat, add the cream and Parmesan cheese, and cook for about 5 minutes until the sauce thickens.
Add the sauce to the pasta and mix well.
When serving, garnish each plate with chopped parsley.
Enjoy this wonderful spaghetti with beef and mushroom sauce!