Bring a large pot of salted water to a rolling boil over high heat. Add the fettuccine and cook until al dente, about 10-12 minutes, then reserve 1 cup of pasta water and drain.

In a large skillet, heat 2 tablespoons of olive oil over medium-high heat. Add sliced fresh mushrooms, season with salt, and sauté until golden brown and tender, about 5-7 minutes. Remove and set aside.

In the same skillet, add more olive oil if needed. Season sliced chicken with salt and pepper, then sauté until golden brown and cooked through, about 6-8 minutes.

In a medium saucepan, combine heavy cream, butter, and crushed garlic over medium-low heat. Whisk continuously for 3-5 minutes until smooth, then gradually stir in Parmesan cheese until thickened.

In a mixing bowl, combine fettuccine, sautéed mushrooms, and chicken. Pour the Alfredo sauce over and toss gently, adding reserved pasta water as necessary to achieve desired consistency.

Serve warm, topped with extra Parmesan cheese and optionally cracked pepper or parsley.