Preheat the oven to 180ºC (350ºF) Gas 4.
Chop the sweet potato and the normal potatoes into bite-sized pieces (leaving the skin on). Put on a baking tray and in the preheated oven for 25 minutes.
Put the coconut milk, together with 400ml water, the ginger, lime juice, maple syrup, curry powder and tamari into a blender, and whiz until everything is smooth.
Chop up the tempeh into small cubes (around 1.5cm), the smaller they are, the more flavour each piece will have. Put the chopped tempeh into a baking dress and dress with approximately half of the dressing. Mixing the tempeh and the sauce well is important to make sure each piece is full of flavour and also that the tempeh is well spread out on the baking tray.
Put the tempeh into the preheated oven and bake for 20 minutes, After 10 minutes, stir the tempeh to ensure that the dressing is well spread and the tempeh is cooking evenly. The tempeh and potatoes should finish cooking around the same time.
Meanwhile, pour in the other half of the dressing in a large sized saucepan - this will become the sauce of the dish along with any remaining sauce from the baked tempeh dish. Bring to the boil and then reduce to a simmer.
Once the tempeh and potatoes are cooked (taste the potatoes and ensure they are fully cooked), transfer them into the pot with the simmering sauce and mix well. Finely chop the pak choi, removing the nub at the end and using the full length of it.
Remove from the heat, taste and season to your taste. Finely slice the spring onion and fresh coriander and sprinkle them over the dish when serving.