1kg is usually two large sweet potatoes. Pick the ones that are slender and long, not the wider ones to reduce the cooking time. Also pick ones that look as similar as possible so that they cook evenly at the same time.
If the purple sweet potato is not as fresh because you have forgotten about it amongst the rest of the vegetables the last two weeks, like I have done before, then the less time it needs to cook. It only took 7min in the microwave in that case.
I’ve used green spring onion before as well and that was really nice too. But you can use whatever you have at home more often.
Adding capers to this salad is also really if you like acidity in salads.