Braised cucumber

This is one of my favourite dishes.

1 pack soybean curd (tofu)
125g peeled prawns, cooked (frozen are cheapest, just defrost for an hour or so before using)
1 large or 2 small cucumbers
4 tablespoons groundnut oil
1 large onion, roughly chopped
1 clove garlic, crushed or finely chopped
1 teaspoon root ginger, finely grated
2 tablespoons soy sauce
1 tablespoon hoisin sauce
1 tablespoon tomato puree
1 teaspoon icing sugar (confectioners' sugar)
salt
1 teaspoon sesame oil (optional)
1 spring onion (scallion), chopped
1 tablespoon chives, finely chopped

Cut the tofu into 1 cm cubes. Remove the ends of the cucumber(s) and halve lengthways. Scoop out the seeds with a teaspoon. Cut the halves into 5 mm slices.
Heat the oil in a wok and fry the onion for 1 minute. Add the garlic and the root ginger stirring well. Add the cucumber, soy sauce, hoisin sauce, tomato puree, prawns, tofu, sugar, pinch of salt and sesame oil if using. Add 3 tablespoons boiling water, stir and simmer gently over moderate heat until most of the liquid has evaporated. Serve hot sprinkled with spring onion and chives.