Roll Italian sausage into small, bite sized balls. Heat a Dutch oven over medium heat; add sausage balls and onion. Sauté until lightly brown and onions become translucent. Add garlic and cook for an additional 2-3 minutes.
Add chicken broth and diced tomatoes with their juice and heat to a boil.
Add chopped spinach and cook for 2-3 mins. Add tortilini. Return to a boil. Reduce heat to medium and cook for 5 mins. Salt and pepper to taste. Serve with grated Parmesan cheese on top