In a mixing bowl, mix panko, 1/4 teaspoon tarragon, 1/4 teaspoon rosemary, and 1/4 teaspoon thyme. Set aside.
In a food processor, grind together paprika, cayenne pepper, celery salt, garlic powder, onion powder, oregano, 1/8 teaspoon rosemary and 1/8 teaspoon thyme. Add mayonnaise and pulse until well combined. Lightly coat the tuna steak with the mayonnaise mixture and then coat the tuna steak in the panko mixture.
Melt butter in a skillet over medium-heat. Add tuna to hot pan and sear on each side for approximately 2 1/2 minutes each or until golden brown.
Meanwhile, in a small skillet, combine all sauce ingredients and reduce over low heat until thickened to a sauce consistency.
Cut a thick wedge of avocado and then slice it to make a fan shape. Spread avocado fan across plate. Place the tuna steak in the center of the plate, pouring shoyu sauce around and on top of it. Garnish with the green onions, tomato concasse, and lemon slice.
To make tomato concasse, make an X-shaped cut on the bottom of the tomato and boil in a pot of water for 15 to 20 seconds. Remove tomato from water, peel off skin, remove seeds, and dice.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.