Wash your tuna steak under cold water, then dry it thoroughly with paper towels. Set aside.
Mix together sesame seeds and pepper. Salt both sides of your steak, then dip into the sesame seeds and pepper—nestle the steak into the seasoning and make sure all sides are covered, including the outside edges.
Heat the sesame oil in a nonstick pan. When oil is hot, lay the steak in and sear for 2 minutes on each side. Use tongs to sear the edges of the steak, too (but only for about 30 seconds). Allow to cool slightly, then, cutting against the grain, slice tuna into ½ inch thick strips.
To assemble the salad, lay down your lettuce and arrange the remaining vegetables and fish on top. Refrigerate and serve cold!
Notes
NOTE: To make a chopped salad, cut your veggies and fish into smaller cubes and pieces.