Cook the tortellini according to the package directions.
While the pasta is cooking, in a large skillet, saute the onion in olive oil until it's tender. Add the garlic and cook for one minute longer. Add the tomatoes, spinach, basil, salt and pepper. Cook the sauce, stirring, over medium heat until the excess liquid has evaporated, about three minutes.
Stir the heavy cream and cheese into the tomato mixture. Bring the pan to a boil, then reduce the heat to medium-low and simmer, uncovered, until the mixture thickens, 8 to 10 minutes.
Drain the cooked tortellini, and toss it with the sauce. Garnish the finished dish with additional Parmesan, if desired.
