In a large pot, heat the olive oil over medium heat. Add the Italian sausage and cook until browned, breaking it up with a spoon, about 5-7 minutes.
Add the diced onion, garlic, carrots, and celery to the pot. Sauté until the vegetables are softened, about 5 minutes.
Stir in the diced tomatoes, chicken broth, ditalini pasta, oregano, basil, salt, and pepper. Bring to a boil, then reduce heat and let simmer for about 10-12 minutes, or until the pasta is al dente.
Add the chopped spinach and cook for an additional 2-3 minutes until wilted.
Remove from heat and stir in the grated Parmesan cheese until melted and well combined.
Serve hot, garnished with fresh parsley and additional Parmesan cheese if desired.