In a bowl, mix ground turkey, breadcrumbs, egg, garlic, parsley, oregano, salt, and pepper.
Shape mixture into small meatballs (about 1 inch).
Heat olive oil in a skillet and lightly brown meatballs (optional but recommended).
Add onion, carrots, celery, garlic, broth, tomatoes, seasoning, and bay leaf to the slow cooker.
Gently add meatballs to the slow cooker.
Cover and cook on LOW for 6–8 hours or HIGH for 3–4 hours.
Add greens or pasta during the last 30 minutes if using.
Adjust seasoning and remove bay leaf before serving.