Finely chop the onion and garlic & parsley. Slice the mushrooms 3 millimeters or 1/8 of an inch thick.
Heat a saucepan with 3 to 4 tbls. olive oil. When hot, saute the onions until they lose there color and become pale. Add the chopped garlic and 2 msk. or 2 tbls. of the chopped parsley. Cook for 1 minute.
Add the mushrooms and gently saute until cooked and lightly browned taking care not to burn the garlic.
Add the tomatoes, salt, sugar and freshly ground pepper to taste.
After adding the tomatoes Simmer sauce for 20 minutes.
As soon as the pasta is cooked strain it and return it to the cooking pot pour over the sauce and transfer to a serving plate adding a bit of the left over sauce and sprinkling on a the remaining parsley.
Serve with freshly grated Parmesan cheese.