Cook the pasta according to package instructions until al dente. Drain and set aside, reserving 1/2 cup of pasta water.
In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté for 3-4 minutes until translucent.
Stir in the minced garlic and sliced mushrooms. Cook for an additional 5-7 minutes until the mushrooms are browned and tender.
Add the fresh spinach to the skillet and cook until wilted, about 2 minutes.
Pour in the heavy cream and sprinkle in the Italian seasoning. Stir to combine and let it simmer for 2-3 minutes until slightly thickened.
Season with salt and pepper to taste. Add the cooked pasta to the skillet, tossing to coat in the creamy sauce. If the sauce is too thick, add reserved pasta water a little at a time until desired consistency is reached.
Stir in the grated Parmesan cheese until melted and well combined. Remove from heat.
Serve immediately, garnished with chopped parsley.