I bring a big pot of salted water to a rolling boil first, since this takes the longest. Once it's bubbling, I drop in the pasta and let it cook until just tender, usually around 7 to 9 minutes. I drain it in a colander and set it aside while I finish the sauce.
While the pasta boils, I heat olive oil in a large skillet over medium heat. I toss in the diced onion and minced garlic and let them cook for 3 to 5 minutes until soft and fragrant. This step builds the flavor foundation for the entire sauce.
Next, I stir in the diced tomatoes with their juices, along with the oregano, basil, crushed red pepper, salt, and black pepper. Then I add the tomato paste and water, stirring until everything blends into a smooth, rich tomato base.
I turn the heat down to low so the sauce doesn't scorch. I cut the cream cheese into small chunks and whisk it in a little at a time. It looks lumpy at first, but keep whisking and it turns silky within a minute or two.
Once the cream cheese has fully melted, I sprinkle in the grated Parmesan and stir until it disappears into the sauce. This is where the sauce really turns thick, glossy, and irresistible.
I add the fresh spinach directly into the skillet and gently fold it through the warm sauce. It only takes 2 to 3 minutes to wilt down completely, so I keep an eye on it and don't overcook it.
Finally, I add the drained pasta straight into the skillet and toss everything together until every piece is coated in that creamy tomato sauce. I taste it, adjust the salt if needed, and serve it warm right away.