Preheat the oven at 180C/356F
Peel the puna yam and cut lengthways or crossways and slice them thinly with a knife or a mandolin slicer.
Add the sliced yam pieces to a bowl, add enough water to cover, add salt to taste, sugar and leave to rest for about half an hour or longer.
Drain the water from the yam and place the sliced yam on a kitchen towel to drain out excess moisture. Add the yam chips to a bowl, add 2 tbsp oil and toss to combine
Place a baking sheet in a baking tray, spread the sliced yam on the tray then place in an oven and bake for 15-25 minutes or till it is well baked.
Take the yam chips out of the oven and place in a bowl, toss in some sugar or salt and leave to cool.