Add onions and garlic to pot and saute for about 5 minutes or until softened.
Add tomatoes, broth, salt and pepper to pot and stir to combine.
Puree soup mixture using an immersion blender or a food processor.
Add rind from Parmesan cheese wedge to mixture, if using.
Bring mixture to a slow boil.
Add pasta shells to soup.
Reduce heat to low and simmer for about 10 minutes.
Remove undissolved rind from soup.
Stir in spinach, reserving some spinach for topping.
Garnish with additional Parmesan cheese and spinach.
Notes
I am partial to boxes of chopped tomatoes that are unsalted and don't contain added preservatives. However, 2 14.5 ounce cans of diced tomatoes can be substituted in this recipe. South Beach Diet Phase 1 - do not add pasta.