In a medium saucepan, heat the bulk Italian sausage over medium heat, using a wooden spoon to break it apart. Cook the sausage for about 5–7 minutes, or until it's browned and no longer pink. Once cooked, carefully drain any excess fat and set the sausage aside.

In the same saucepan, add the sliced onion and sauté over medium heat for 3–4 minutes until it becomes tender and translucent, stirring occasionally. Next, add the minced garlic and continue cooking for another minute.

Pour in the reduced-sodium chicken broth and water, then stir to combine. Bring the mixture to a boil over high heat. Once boiling, reduce the heat to low and let it simmer uncovered for about 10 minutes.

Return the broth to a boil over medium-high heat, then gently stir in the fresh spinach and cheese tortellini. Cook for 7-9 minutes, or until the tortellini are tender and float to the top.

Once the tortellini are cooked to perfection, ladle the soup into bowls. Top each serving generously with shredded Parmesan cheese and sprinkle with crushed red pepper flakes.