In a large saucepan, heat the oil and saute the yam pieces over a medium heat until they are golden brown. Remove from pan with slotted spoon.
Reduce the heat and in the same oil, saute chilli, coriander, onion, tomato, carrot, garlic and spices until the onion gets translucent. Season with salt and pepper. Add the coconut milk and the stock and bring to the boil. Add the bay leaves, then lower the heat to a simmer. Stir in the cornflour mixture. Add the yams and bananas. Cover and simmer gently for 30 minutes. Remove from heat, check the seasoning, remove the bay leaves and allow 10 minutes for the stew to rest before serving with rice.