In a large pot over medium-high heat, add in the olive oil. Once hot, sauté the onion until tender, about 3 minutes. Add in the sliced mushrooms and cook, stirring frequently, for an additional 3 minutes. Stir in the garlic, Italian seasoning, salt and pepper and cook until fragrant, about 30 seconds.
To the large pot, add in the meatballs, chicken broth, water and spaghetti sauce. Bring the mixture to a boil. If using frozen meatballs, bringing it to a boil will take a little bit extra time.
Once the soup is boiling, add in the tortellini, and cook until al dente, about 7 minutes. Serve the soup garnished with freshly chopped parsley or basil and grated parmesan cheese. Enjoy!
Notes
MAKE AHEAD:If preparing soup ahead of time, do not add the tortellini to the soup. Omit the 2 cups of water from the recipe and instead cook the tortellini in a separate pot of water until al dente. Drain the tortellini and store separate from the meatball soup base. Just before serving, combine the two and reheat. You can refrigerate the soup for up to 4 days.