In a bowl, combine ground beef, breadcrumbs, egg, minced garlic, salt, and pepper. Mix gently and form into golf ball-sized meatballs.

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

Stir in canned tomatoes and chicken broth. Bring to a gentle simmer.

Carefully drop meatballs into the simmering soup. 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.