Soak the dried mushrooms in boiling water for 8–10 minutes or until soft. Cut off and discard the stalks, then drain. Use a pestle and mortar to grind and pound the garlic and coriander roots and stalks into a paste. Mix the minced prawns with the garlic paste, cornflour, salt and pepper.
Spoon the prawn mixture into the melon rings (don't overstuff the rings or they might explode during cooking). Use a cocktail stick to poke through one side of the bitter melon and out the other side. This will secure the filling inside the ring. Repeat, using the rest of the bitter melon and filling.
Prepare the whole prawns (see
Put the stock, goji berries (if using), soy sauce and preserved radish in a pan and bring to the boil. Reduce the heat to low and add the stuffed melon and mushrooms. Cook for 10–12 minutes or until the melon is tender. Add the prawns 3–4 minutes before the end of the cooking time. Taste and adjust the seasoning. Leave the sticks on the melon pieces or pull them out. Spoon into serving bowls and garnish with spring onions and coriander.