Pre-heat oven to 375F.
In a large pot of boiling salted water, cook pasta according to package instructions; drain well. Set aside.
Melt butter in a large skillet over medium heat. onion and mushrooms, cook for 2-3 minute or until the mushrooms are soft and tender. Add garlic, spinach, italian seasoning, and salt + pepper. cook for another minute.
Whisk in flour until lightly browned, about 1 minute. Gradually whisk in vegetable broth and then cream, and cook, whisking constantly, until incorporated, about 1-2 minutes. Stir in parmesan just before turning off heat.
Pour cooked pasta into a large 13x9 baking dish. Top with spinach mushroom cream sauce. Drizzle with mozzarella cheese. Bake for 18-20 minutes or until bubbly.