Cook the fettuccine pasta according to the package instructions until al dente. Drain and set aside, reserving 1 cup of pasta water.
In a large skillet, heat the olive oil and butter over medium heat. Add the sliced mushrooms and sauté for about 5 minutes, until they are golden and tender.
Stir in the minced garlic and cook for another minute, until fragrant.
Add the fresh spinach to the skillet and cook until wilted, about 2-3 minutes.
Pour in the heavy cream, stirring to combine. Bring the mixture to a gentle simmer.
Add the grated Parmesan cheese, Italian seasoning, and reserved pasta water, stirring until the cheese melts and the sauce thickens.
Season with salt and pepper to taste.
Toss the cooked fettuccine in the creamy mushroom-spinach sauce until well coated.
Serve immediately, garnished with fresh parsley and additional Parmesan cheese if desired.