Sauté the Aromatics: Heat the olive oil in a large pot over medium heat. Add the diced onion and cook for 3-4 minutes until softened. Stir in the garlic and cook for another minute until fragrant.
Add Veggies and Seasoning: Toss in the carrots, celery, and Italian seasoning. Cook for 5 minutes, stirring occasionally, until the vegetables begin to soften.
Build the Broth: Pour in the diced tomatoes (with their juice) and the broth. Stir to combine, then bring the mixture to a gentle boil.
Cook the Tortellini: Add the tortellini to the pot and cook according to the package instructions, usually 5-7 minutes, until they’re tender and floating.
Add Greens and Cream: Stir in the spinach or kale and let it wilt for 1-2 minutes. If using cream, add it now and stir until the soup is silky and warmed through. Avoid boiling after adding cream to prevent curdling.
Season and Serve: Taste and adjust seasoning with salt and pepper. Ladle the soup into bowls, sprinkle with Parmesan cheese and fresh herbs, and serve with crusty bread for dipping.