While the tofu is steaming, mix the water, cornstarch and light soy sauce together to make the seasoning.
Heat the vegetable oil in a wok and sauté the garlic until fragrant.
Add the preserved radish and sauté until fragrant, then add the prawns and cook for 1 to 2 minutes until they turn pinkish.
Pour in the seasoning and cook until the sauce thickens.
Tip: Pour the sauce carefully — it's hot. You can remove the steamed tofu from the stove first before pouring, and tip off any excess water on the plate if you prefer a less diluted sauce.