Method:

1. Assemble the Steamer
   Add water to the base of a steamer or wok and position the steamer basket or insert on top. Do not turn on the heat yet.
2. Make the Soy Mixture
   Place a shallow heatproof bowl inside the steamer. Add the tamari light soy sauce, water and cooking oil, then stir to combine.
3. Add the Eggs
   Crack the eggs whole into the soy mixture, taking care not to break the yolks.
4. Steam the Eggs
   Cover with the steamer lid, then turn on the heat and bring the water to the boil.
   Once boiling, cook the eggs for 5-6 minutes, or until the whites are set and the yolks are cooked to your liking.
   The water will take approximately 3–4 minutes to reach boiling point before the timed cooking begins.
5. Garnish and Serve
   Carefully remove the hot bowl, scatter over the green onions, chilli oil and serve immediately. Optional to serve alongside steamed rice or Chang's Vermicelli Rice Noodles.

Five minutes steaming should give you set whites with soft yolks.
For completely firm yolks, I’d allow 8 minutes.

Please note: the bowl depth and steam intensity will affect the cooking time.