In a large bowl, combine ground chicken, breadcrumbs, Parmesan cheese, egg, garlic, onion, parsley, and spices. Mix gently until just combined to maintain a soft texture.
Shape the mixture into small, even-sized meatballs to ensure they cook evenly and retain their structure.
Heat olive oil in a skillet over medium heat until it shimmers, ensuring proper browning during cooking.
Cook the meatballs in batches, turning occasionally, until they are golden brown and fully cooked through.
Add tomato sauce if desired and simmer briefly to enhance flavor and moisture.
Let the meatballs rest before serving to keep them juicy and tender.