Cook the pasta according to package directions. Drain and set aside.
Heat olive oil and butter in a large skillet over medium heat.
Add garlic and onion, sauté for 2–3 minutes until fragrant and translucent.
Add mushrooms, cook for 5–7 minutes until they release moisture and start to brown.
Toss in the spinach and cook until wilted.
Pour in the heavy cream and stir in Parmesan cheese. Let it simmer for 2–3 minutes.
Season with salt, pepper, and Italian seasoning (if using).
Add the cooked pasta to the skillet and toss until fully coated in the sauce.
Serve hot, garnished with chopped parsley and red pepper flakes if desired.