Heat vegetable oil in a deep-fryer or large wok to 180°C/350°F and fry crab quarters for about 1 minute, or until shells change colour. Remove from oil and set aside.
In a separate wok, heat extra oil, add spice paste and stir-fry for 1 minute over high heat to release flavours.
Add oyster sauce and crab pieces and toss over heat until crab is well co