Preheat the oven to 200c/400f. Pierce the potatoes with a fork, then place in the oven for 40-45 minutes until cooked throughout.
Whilst the potatoes are cooking mix the peanut butter, lime juice, soy sauce, half of the chilli, coconut milk, brown sugar, ground coriander, half the spring onions and lemon grass paste until combined.
When the potatoes are cooked, take out of the oven and leave to cool for 10 minutes (leave the oven on). Cut the potatoes in half lengthways and scoop out all of the potato into a bowl. Place the skins on a baking tray and place back in the oven for 5 minutes to crisp up.
Combine the peanut butter sauce mix with the sweet potato filling and mix using a fork. Take the potato skins out of the oven, and fill with the peanut/potato mixture. Place back in the oven for 10 minutes to heat through.
Take out of the oven and place on a plate. Top with the reserved chopped chilli, spring onions and the peanuts,then serve.