Pre-heat the oven to 220°C (fan). Add the tomatillos, peppers, chillies, garlic and onion to a baking pan. Roast in the oven for 15 minutes until the skins are blistered and starting to char.
Once roasted allow to cool slightly and then add to a blender along with the remaining coriander, cumin, oregano and chicken stock. Blend until smooth.
Heat the oil in a pan and add the chicken chunks. Cook on a medium heat for 5 minutes until browned all over. Add the blended sauce and the salt, turn the heat down to low, cover with a lid and simmer for 30 minutes until the chicken is fully cooked and tender.