1) In a mixing bowl, mix the panko, 1/4 teaspoon tarragon, 1/4 teaspoon rosemary and 1/4 teaspoon thyme. Set aside.
2) In a food processor, grind together the paprika, cayenne pepper, celery salt, garlic powder, onion powder, oregano, 1/8 teaspoon rosemary and 1/8 teaspoon thyme. Add the 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.
3) Melt the butter in a skillet over medium-heat. Add the tuna to the hot pan and sear on each side for approximately 2 1/2 minutes each or until golden brown.
4) Meanwhile, in a small skillet, combine all of the sauce ingredients and reduce over low heat until thickened to a sauce consistency.
5) Cut a thick wedge of avocado and then slice it to make a fan shape. Spread the avocado fan across plate. Place the tuna steak in the centre of the plate, pouring the shoyu sauce around and on top of it.
Garnish with the green onions, tomato concasse and lemon slice.
*Cook's note: To make the tomato concasse, make an X-shaped cut on the bottom of the tomato and boil in a saucepan of water for 15 to 20 seconds. Remove the tomato from the water, peel off the skin, remove the seeds and dice.