Mix Together The Mayonnaise, Wasabi Paste, Five-Spice Powder, And 1 Tablespoon Soy Sauce In A Small Bowl. Lay The Tuna Fillets Into A Glass Baking Dish. Pour The Rice Vinegar And 1 Tablespoon Soy Sauce Over The Tuna. Spread The Mayonnaise Mixture Evenly Over Both Sides Of Each Piece Of Fish. Cover The Dish And Refrigerate 15 To 30 Minutes. Prepare A Skillet With Cooking Spray And Place Over Medium-High Heat. Sprinkle The Sesame Seeds Evenly Over Both Sides Of The Fillets. Lay The Tuna Gently Into The Skillet. Grill To Desired Level Of Doneness, About 2 Minutes Per Side For Medium-Rare. Serve Immediately.