Mix together the pork, prawns, spring onions, chilli, garlic, ginger, oyster sauce, sesame oil and water chestnuts with your fingers in a bowl until well combined.
Lay a wonton wrapper in the palm of one hand. Place 1 teaspoonful of the pork mixture in the centre. Dampen the wrapper edges with water and bring up the sides, then press them around the filling, leaving the filling exposed. Gently tap on the work surface to create a flat base. Repeat with the remaining wrappers and pork mixture. (You can refrigerate on a tray lined with nonstick baking paper for up to 1 hour before cooking.)
Combine all the ingredients for the sauce in a small bowl.
Place the dumplings without touching in stacking bamboo steamer baskets lined with nonstick baking paper, cover and steam over a wok or large saucepan of boiling water (see
Serve the dumplings with the sauce for dipping.