Heat the oil in a large frying pan over high heat.
Cook the chicken until it has browned all over.
Add the onion, garlic and curry powder.
Cook for a few minutes until the onions have softened.
Season with salt and pepper.
Add the coconut milk, chicken stock and fish sauce.
Stir through the potatoes, sweet potatoes and frozen peas (no need to defrost).
Cook for 20-30 minutes on low-medium heat, or until the potatoes and sweet potatoes have cooked through.
Taste the sauce for seasoning.
Turn the stove up to medium-high heat, and stir through some of the cornflour (cornstarch) slurry. You may not need all of it. You only need just enough to thicken the sauce so that you have a thick mixture. Alternatively, if your sauce is already too thick or too concentrated, add some boiling water.
Taste for seasoning again, and add some lime juice to taste (optional).
Once you are happy with the seasoning, stir through the coriander (cilantro).
Transfer the filling to a bowl or plate, and set aside to cool completely. The filling will thicken more upon cooling.