Mix wasabi and crème fraîche, season with a little salt. Wash the lime hot, dab dry and finely grate the peel. Halve the lime and squeeze 1 half. Cut the rest of the lime half into pieces.
Clean and wash spring onions and cut into fine rings. Cut the chilli lengthwise, remove seeds, wash and finely chop. Peel and grate ginger.
Wash the fish, dab dry and dice very finely. Mix with chilli, spring onions, ginger, 2 tablespoons of oil, lime zest and juice. Season to taste with a little salt.
For the vinaigrette season the vinegar with salt, pepper and 1 pinch of sugar. Fold in 2 tablespoons of oil. Clean, wash and drain the salad. Arrange on plates and sprinkle with vinaigrette. Arrange the salmon tartar in a starter ring (approx. 8 cm Ø; alternatively fold four rings of aluminium foil) on top.
Spread 1 blob each of wasabi cream and lime pieces around the tartar.