Heat the oil in a large saucepan on a medium-high heat. Cook the chicken until lightly browned.
Reduce heat to medium. Add the onion, green pepper, potato and sweet potato. Cover and cook for 5 minutes, stirring occasionally, until veg begins to soften.
Add the garlic and chillies. Cook for 1 minute. Add tomatoes, oregano, salt, pepper and half the coriander. Cook for 1 minute.
Pour in the stock. Bring to the boil, then cover and simmer over a low-medium heat until the chicken is cooked through and the vegetables are tender, 15 to 20 minutes. (If serving with rice, cook that now.)
Sprinkle with the remaining coriander just before serving. Serve with rice or fajitas.
Depending on who I'm making this for I alter the amounts of chilli and pepper. If you're unsure of how hot you can handle, try using just 1 chilli and 1 to 2 teaspoons pepper. Taste at end of cooking and add more pepper if desired.