Heat the oil in a wok over medium heat. Cook and stir the onions and garlic in the hot oil until tender. Mix in the rice, sugar and salt, and cook 5 minutes, until well blended. Stir in the egg until the rice is coated. Increase heat to high, and mix in the crabmeat, spring onions and coriander. Continue cooking 2 to 5 minutes, until the crab is heated through. Garnish with the cucumber and lime slices to serve.