Prepare the meatballs by combining ground beef, breadcrumbs, egg, minced garlic, salt, and pepper in a bowl. Mix gently and form into golf ball-sized meatballs.

In a large pot over medium heat, add olive oil and sauté chopped onion until translucent; then add diced carrots and celery and cook until softened.

Stir in canned tomatoes and chicken broth to build the soup base. Bring to a gentle simmer.

Carefully drop meatballs into the simmering soup and cook for 15-20 minutes until fully cooked.

Taste and adjust seasoning; add spinach or kale if desired.

Ladle into bowls and garnish with parsley if desired.