1. In a medium-sized saucepan, bring 450ml water to a boil over high heat. Add the tofu and return to the boil. With a slotted spoon, remove the tofu and place on a rack to cool.
2. Remove all stems from the spinach. Wash spinach in several changes of cold water and drain thoroughly in a colander. Return water to the boil over high heat and add the spinach.
3. Cook until limp, about 30 seconds. Drain and rinse under cold water.
4. Squeeze the spinach to remove excess water and form into a tight ball. Chop the spinach by cutting the ball into small slices. Place spinach into a large bowl.
5. Cut the tofu into tiny diced pieces. Finely chop the prawns. Add the sesame oil, salt, tofu and prawns to the spinach and toss to combine.
6. Chill, if desired, or serve at room temperature.