In a large pot or Dutch oven, heat the olive oil over medium heat. Add the Italian sausage and cook until browned, breaking it apart with a wooden spoon, about 5-7 minutes. Drain excess fat if necessary.
Add the diced onion, carrots, and celery to the pot. Cook for 3-5 minutes, or until the vegetables start to soften.
Stir in the minced garlic and cook for an additional 1 minute, until fragrant.
Pour in the chicken broth and diced tomatoes, and add the dried basil, dried oregano, salt, and pepper. Bring the mixture to a boil.
Once boiling, reduce the heat to a simmer and add the tortellini. Cook according to package instructions, typically around 5-7 minutes.
In the last minute of cooking, add the chopped spinach to the soup and stir until wilted.
Taste and adjust seasoning if necessary. Serve hot, garnished with grated Parmesan cheese if desired.