Bring a large pot of salted water to a boil, add the pasta, and cook according to package instructions until al dente, about 8-10 minutes. Drain and set aside.

In a skillet, heat olive oil over medium heat, add chopped onion, and sauté for 2-3 minutes until translucent. Transfer to a plate.

Add another tablespoon of olive oil, toss in sliced mushrooms, and cook for about 3 minutes until golden brown. Transfer to the plate with onions.

In the same skillet, add fresh spinach and cook for about 2 minutes until wilted. Transfer to the plate.

Add minced garlic to the skillet and sauté for 30 seconds until fragrant. Pour in vegetable broth and scrape the bottom of the skillet.

Lower the heat, stir in heavy cream and grated Parmesan cheese, add chili flakes, and Italian seasoning, and simmer for about 2 minutes until slightly thickened.

Return the cooked pasta, sautéed onions, mushrooms, and spinach to the skillet. Toss gently to combine, adding reserved pasta water if needed.

Adjust seasoning with salt and pepper, serve warm, and garnish with additional Parmesan if desired.