In a food processor, combine celery, lettuce, coriander, tomatoes, serrano chillies, poblano chilli, garlic, peppercorns, cloves and cumin. Add enough chicken stock to make a thin paste. Pour into a saucepan and simmer over low heat.
Heat one tablespoon oil in a frypan and fry the sunflower seeds until golden. Crush and add to the sauce.
Simmer the sauce to your desired consistency, then add the pork and heat through.