If using roasted sweet potatoes heat oven to 200ºC, pour the olive oil into a shallow roast dish and heat for 5-10 minutes. Tip the diced sweet potatoes into the hot oil and disturb them so they're well coated. Roast the sweet potato for 40 minutes, turning frequently. After cooking set aside. For a healthier option, don't roast, but add the diced sweet potatoes to the boiling coconut milk and thai paste mix, 5 minutes before the onions.