Fry onions for 5 mins
Add garlic, ginger, coriander, cumin and cayenne pepper. Fry on a low heat for 1 minute.
Pour in chopped tomatoes, peanut butter and chicken stock. Stir until peanut butter has dissolved. Add chicken and simmer for 30 mins. Stir frequently to prevent the peanut butter sticking to the bottom of the pan.
Stir in sweet potato, red pepper and fish if using. Simmer for another 30 mins.
Scatter with chopped coriander and serve with rice balls and lime wedges.