Bring a large pot of salted water to a boil. Add the tortellini and cook according to package instructions until just tender. Reserve some of the pasta water before draining.

Meanwhile, add the olive oil to a large skillet over medium heat. Add the onion and sauté for about 5 minutes, until the onion is translucent.

Stir in the roasted red pepper and spinach and cook until wilted, about 2 minutes. Then add the diced tomatoes (with their juices). Let the mixture simmer for 5 minutes, allowing the flavors to meld and the sauce to reduce slightly.

Pour in the heavy cream. Stir and allow it to thicken slightly, about 3-5 minutes. Then add the Parmesan cheese, stirring until melted and the sauce is smooth and creamy. Season with salt, pepper.

Add the cooked tortellini to the skillet and gently toss to coat the pasta evenly with the creamy sauce.

Serve immediately, garnished with extra Parmesan cheese if desired.