Heat the oil in a large skillet or wok over medium-high heat. Add the onion and ginger and cook 1-2 minutes. Add the black bean sauce and stock and bring to a boil. Add the crab and toss to coat in the black bean mixture. Cover and cook 5 minutes, or until the crab is just heated through. Spoon the crab on to a serving platter, sprinkle with green onions and serve.
Note: If desired, our seafood staff can clean the cooked crab for you.