Bring a large pot of water to a boil and add salt. Add the pasta and cook until al dente (8-10 minutes). Reserve 1 cup of the pasta water and drain the pasta.

Heat the olive oil in a large skillet over medium heat. Sauté the diced onion and minced garlic for 3-4 minutes until the onion is soft. Stir in the diced tomatoes, Italian seasoning, red pepper flakes, salt, and black pepper.

Let the sauce simmer for about 3 minutes. Lower the heat and add the tomato paste and cream cheese, stirring until it melts into a smooth, creamy sauce. Add the baby spinach and cook until wilted, about 2 minutes.

Add the cooked pasta and Parmesan and stir thoroughly, adding as much reserved pasta water as needed to achieve your preferred sauce consistency. Let it simmer briefly, then top with extra grated Parmesan cheese prior to serving.