Coat tuna with sesame oil, salt and pepper. On a hot cooking surface sear tuna for 2 minutes on each side for rare. Slice into strips, once cooked.
Combine wasabi, rice vinegar, soy sauce and olive oil. Whisk to combine. Mix the dressing with the lettuce, reserving a small amount to pour over tuna.
To serve, place 1/2 of the coated lettuce on each plate. Place 1/2 of the peppers, cucumber and tomatoes on lettuce. Place 1/2 of the sliced tuna on top of lettuce and vegetables on each plate. Drizzle reserved dressing over tuna.