Heat the olive oil in a large pot or Dutch oven over medium heat. Add the Italian sausage and cook, breaking it up with a spoon, until browned. Drain off any excess grease.
Add the chopped onion to the pot and cook until softened, about 5 minutes. Add the minced garlic and cook for 1 minute more until fragrant.
Pour in the chicken broth and add the diced tomatoes (with their juice), Italian seasoning, salt, and pepper. Bring the mixture to a simmer.
Add the refrigerated tortellini to the simmering broth. Cook according to package directions, usually about 5 to 7 minutes, until the tortellini are tender.
Stir in the fresh spinach until it wilts into the soup, about 1 minute.
Reduce the heat to low. Stir in the heavy cream and grated Parmesan cheese until the soup is creamy and heated through. Do not let the soup boil after adding the cream.
Serve immediately. This is a great comfort food soup dinner.
Notes
For a slightly different flavor, substitute ground turkey for the Italian sausage.
If you prefer a less rich soup, substitute half-and-half for the heavy cream.
This recipe makes a wonderful one pot pasta soup that freezes well for later meals.