Blend vinegar, soy sauce, ginger, garlic, wasabi (or horseradish and mustard seeds), sugar, and green onion. Taste sauce, adjust seasoning if necessary (adding more soy, sugar, ginger etc if preferred). Marinate tuna steaks in blended sauce for about 10 minutes.
While tuna is marinating, prepare your wraps.
First, mix together the yogurt and cayenne (adding spice to taste). Set sauce aside.
Toss cabbage and carrots together, and set aside.
Heat flour tortillas for 10 seconds in a microwave.
Assemble the wraps-- For each wrap, start with the tortilla, then add one piece of lettuce, then ¼ the cole slaw, and ¼ the yogurt sauce.
Next, sear the tuna. Heat oil in a heavy bottom pan (like a cast iron pan) on high, until oil is very hot. Reserving marinade for later, remove steaks from marinade, and sprinkle both sides of the tuna with sesame seeds.
Sear tuna for 15-30 seconds per side, then remove from pan. Reduce heat to medium and allow pan to cool slightly. Add marinade to pan with lemon juice, and stir with a wooden spoon. Allow sauce to thicken, and then spoon ¼ sauce over each wrap. Add any remaining green onion if desired.
Cut the tuna steaks into long thin strips, and then divide among the wraps. Roll the wraps and fold the ends in. Serve immediately.