Preheat the slow cooker if necessary. Heat the oil in a skillet, add the chicken a few pieces at a time until they are all in the pan. Fry, stirring until golden. Remove the chicken from the pan with a slotted spoon and place it in the slow cooker.
Add the onions, chilies, ginger and curry paste to the skillet and fry, stirring for 2-3 minutes. Pour in the coconut cream or coconut milk, stock and ground almonds. Tear half the cilantro into pieces and add to the sauce with a little salt and pepper. Bring to a boil, stirring contstantly, then spoon over the chicken.
Cover with a lid and cook on low 6-8 hours. Stir the korma, then ladle it into bowls, top with spoonfuls of yogurt, the tomatoes, and extra raw onion and the remaining cilantro, torn into small pieces. If desired, serve over rice. Serve with warm chapattis.