Clean crabs, then open shell and remove the two big claws. Cut each crab into two pieces, then cut again into 8 small pieces. Crush big claws with back of cleaver and cut each into two pieces.
Dust crab with flour, then drop into hot oil and deep-fry for about 1 minute. Remove.
Heat 3 tablespoons oil in frying pan. Stir-fry green onion, ginger, and ca