Bring a large pot of water to boiling. Add the spaghettini and boil until al dente, 7 to 9 minutes. Drain, reserving some of the water, and set aside.

While the spaghettini is boiling, heat olive oil in a medium skillet over medium low heat. Once thoroughly heated, add garlic and cook until fragrant, 30 seconds to 1 minute. Add the sliced mushrooms and salt. Saute until the mushrooms start to brown, 5-7 minutes.

Toss with the drained pasta. If the spaghettini is too dry, add some of the reserved water. Season with chopped parsley, ground pepper, and garnish with freshly grated Parmesan.