Pat the ahi tuna steaks dry with a paper towel. Place the soy sauce and tuna in a bowl and set aside.
Heat the oil in non-stick pan on medium-high heat until very hot.
Coat the tuna well with the panko breadcrumbs. Sear the tuna for 1 minute on each side for rare; 2 minutes on each side for medium-rare; or 3 minutes on each side for medium. (If desiring medium-well or well-done sear the outside of the tuna in the pan 1 minute per each side and finish in a 350-degree oven on a baking sheet for 5 - 6 minutes so the tuna does not burn)
Remove the tuna from the pan to a cutting board and allow to rest for 5 minutes before slicing.
Dampen the nori sheet with water so it becomes flexible. Lay the nori sheet on a cutting board and spread a thin layer of the cooled rice (see recipe, cool the rice completely before spreading onto the nori) onto the nori sheet. Layer with shaved cucumber, sliced avocado, and sliced tuna. Gently roll up the nori sheet. Dampen an additional nori sheet and roll up to double wrap the roll. Then set aside. (Repeat this process with any additional sushi rolls)
In a bowl whisk together all of the ingredients for the Yum Yum Sauce.
Slice the sushi rolls about 1/2 inch thick, drizzle with yum yum sauce, garnish with wasabi, pickled ginger, and scallions.