In a zip top bag, combine soy sauce, sesame oil, and 2 tbsp. Asian Style Sesame Sprinkle. Add tuna steaks and marinate for 1-2 hours. Remove tuna from marinade and dust with remaining 1 tbsp. Asian Style Sesame Sprinkle. Sear on high heat (either on grill or in sauté pan) for 30 seconds per side, longer for more well-done meat. Remove from heat and slice against the grain in thin slices. Arrange on plate and set aside.
For the wasabi cream, combine the sour cream, wasabi powder and rice wine vinegar. Mix thoroughly until a smooth and creamy green paste is achieved.
Serve with sushi rice and a dollop of wasabi cream on each slice of seared tuna.