Prepare the wasabi mayonnaise ahead of time so it can develop its full flavor. Mix the mayonnaise, lemon juice (or rice vinegar) and soy sauce. When blended well, add the wasabi powder and blend. Cover and refrigerate for at least 1 hour.
Marinade tuna filets in the teriyaki and lime juice for 30 minutes. Remove filets from marinade and drain. Mix black pepper and sesame seeds on large plate. Drizzle olive oil on filets, then mash filets firmly on the sesame seed and black pepper mixture to form a crust. Flip and do the same to the other side of the tuna.
Heat cast iron skillet on very high heat. The pan can be lightly sprayed with Pam if desired but not necessary since the sesame seeds will prevent the fish from sticking. Tuna is most flavorful when rate inside so cooking time is short, only 2 to 3 minutes on each side. The seeds will blacken on the outside giving a wonderful nutty flavor.
Remove to a serving plate and spoon warmed wasabi mayo over the filets.
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