Heat the oil in a Dutch oven over medium heat. Cook the onion 4 minutes, then add the garlic and Italian seasoning and cook 30 seconds.
Add the tomatoes with their juice and the broth. Bring to a rolling boil.
Add the tortellini and cook according to the package time, usually 3 to 5 minutes. Start checking early; refrigerated pasta goes from tender to mushy fast.
Turn off the heat and stir in the spinach. It wilts in the residual heat in under a minute.
Stir in the cream if using, season, and serve with Parmesan on top.