Heat a saucepan of water on the hob and place a steamer on top.
Place the garlic, chilli, ginger and sunflower oil in a small bowl and mix.
Chop up the crab, remove the brown meat and discard the dead manâ€™s fingers (gills). Place the meat in the steamer for 4-5 minutes.
Meanwhile, add two tablespoons of the flavoured oil to a wok set over a high heat. Fry without colouring, then add the tomato ketchup, yeast extract and soy sauce. When it starts to caramelise, add the crab and toss until coated.
Add 150ml/5fl oz water, cover with a lid and cook for a further three minutes.
Remove from the heat, add the spring onion and coriander and serve immediately.