Peel the sweet potatoes, then chop them into bite-sized cubes. Cook in hot, lightly salted water until soft (for about 8 minutes).
In the meantime, chop the onion, wash the cabbage and thinly slice it.
Using a slotted spoon, remove the boiled sweet potato pieces, then cook the cabbage in the same water for 2-3 minutes and drain.
Heat the olive oil in a pan, soften the onions for about 5 minutes, then add the sweet potato and cabbage pieces together with the soy sauce. Stir-fry for a couple of minutes, then form 2 small wells in the middle. Open the egg shells and carefully slide the eggs into the wells.
Saute, under cover, for about 8-10 minutes, depending on how runny you like your egg yolk.
Season with salt and pepper, then serve.