In a large pot, heat a tablespoon of olive oil over medium heat.
Add the diced onions and sauté until translucent, about 3-4 minutes.
Add the minced garlic and sauté for another minute until fragrant.
Crumble the Italian sausage into the pot and cook until browned, about 5-7 minutes.
Pour in the chicken broth and add the diced tomatoes (with juices).
Stir in the Italian seasoning, salt, and pepper.
Bring the mixture to a boil, then reduce heat to simmer.
Add the tortellini and cook according to package instructions, usually about 5-7 minutes.
Stir in the fresh spinach and cook until wilted, about 1-2 minutes.
Serve hot, garnished with fresh parsley.