Add olive oil to a large Dutch oven or soup pot. Heat over medium, then add the onions, carrots, celery and a few pinches of kosher salt. Cook for 10 to 12 minutes or until tender, then add in the garlic and cook for 1 minute before adding in the chopped tomato and cook for an additional 2 to 3 minutes.
Add in the crushed tomato sauce and pour in the broth, stir and bring to a simmer. Once bubbling; cover, reduce heat to low and cook for 30 minutes.
Next add in the cooked rice and baby spinach, stir until the spinach has wilted and rice is heated through. Lastly, season with salt and pepper.
Ladle soup into bowls and top with Parmesan Reggiano, minced parsley and extra freshly ground black pepper.