In a large pot or Dutch oven, heat olive oil over medium-high heat. Add the sausage, onion, and garlic. Cook, stirring and breaking up the meat with a wooden spoon, until the sausage is no longer pink, about 5-7 minutes. Drain off excess grease.
Stir in the broth, diced tomatoes, tomato sauce, and Italian seasoning. Bring to a boil; cover, reduce the heat to low, and simmer (covered) for 15 minutes.
Remove the lid, add the tortellini, and cook just until tender, about 5-7 more minutes. Stir in Parmesan cheese. Taste and season with salt and pepper, if necessary.
Serve soup immediately, and garnish with additional cheese and fresh herbs.