Heat the oil in a saucepan, add the onion and fry gently for 5 minutes until softened and just beginning to turn golden. Stir in the chilli, red pepper, garlic, carrot, potato and herbs and fry for 5 minutes, stirring.
Pour in the coconut milk and beef stock, then season with salt and cayenne pepper. Bring to the boil, stirring, then cover and simmer for 30 minutes or until the vegetables are tender. Discard the herbs, then taste and adjust the seasoning if needed.
Rub the steak with the oil then season lightly with salt and cayenne pepper. Heat a griddle or frying pan and when hot add the steak and fry for 2–5 minutes on each side to taste. Leave to stand for 5 minutes then slice thinly. Ladle the soup into bowls, garnish with the steak slices and serve with crusty bread.