Halve eggplants lengthwise and brush with oil. Barbecue or grill, turning frequently until flesh softens completely and skin darkens. Carefully peel off skins and discard but retain split stem for decorative purpose. Keep eggplant boats warm in oven.
Fry two-thirds of spring onions in oil until golden. Add sauce ingredients, cook until sugar is dissolved then add crab meat and heat through.