Boil water in a large sauce pan.
Put noodles in boiling water and cook for 2 minutes. Drain. Run cool water over noodles.
Combine the oils, lime juice and wasabi paste and pour over noodles.
Add the pickled ginger and chives and toss.
Put sesame seeds on a flat plate. Press seeds into tuna until tuna is well coated.
Heat a non-stick frying pan over high heat.
Cook tuna on each side for 1 minute each or until just seared. Cut tuna into 3/4 inch slices.
Divide the noodles among 4 large bowls and top with tuna.
Serve with soy sauce and a small dab of wasabi in a separate dipping bowl.