Bring the broth, water, and marinara sauce to a boil over high heat. Add the meatballs, and as soon as the liquid starts to boil again, add the pasta.
Adjust the heat to medium to maintain a simmer. Cover and simmer the soup for 5 minutes. Uncover and simmer the soup for 6 to 7 minutes or until the pasta is tender.
Add the two tablespoons of parsley to the soup and stir. Garnish each serving with the grated cheese and the rest of the parsley.
Notes
Choose smaller frozen meatballs, approximately 1/2-ounce to 1-ounce. I use beef meatballs, but you can also use turkey meatballs.This soup is best not long after it's made because the pasta will soak up the broth if it sits too long. Any leftovers will be delicious but not as soupy.Recipe adapted from Skinnytaste