1.Lift flap under body of each crab; turn crab over, hold body with one hand while pulling off top part of shell with the other. Discard shell and gills on either side of body. Rinse crab under cold water; chop body in half.
2.Place lemon grass, ginger and herbs in large baking-paper-lined steamer, over large saucepan of simmering water; top with crab. Cook about 10 minutes or until crab is changed in colour.
3.Make fennel salad. Segment oranges over small bowl; reserve juice. Using mandolin or V-slicer, cut fennel into paper-thin slices. Combine fennel, reserved juice, vinegar and oil in large bowl. Add radicchio, chervil and orange segments; toss gently.
4.Serve crab with fennel salad.