In a large mixing bowl, combine the ground beef (or turkey), breadcrumbs, Parmesan cheese, egg, minced garlic, Italian seasoning, salt, and pepper. Mix until well combined, then shape into small meatballs (about 1 inch in diameter). Set aside.
Heat olive oil in a large pot or Dutch oven over medium heat. Add the diced onion, carrots, and celery. Sauté for 5-7 minutes, until the vegetables begin to soften and the onion is translucent.
Carefully add the meatballs to the pot, cooking until browned on all sides (about 5 minutes). They do not need to be fully cooked through at this point.
Pour in the beef broth and diced tomatoes with their juice. Stir to distribute the ingredients evenly.
Bring the stew to a simmer, then reduce heat to low. Add the green beans and cover the pot. Let it cook for about 20 minutes, allowing the flavors to meld and the meatballs to cook through.
Once cooked, taste and adjust seasoning with salt and pepper, if necessary.
Serve hot, garnished with fresh chopped parsley.
Notes
Feel free to substitute ground turkey for ground beef if desired.