Combine aioli, sour cream, pickle relish, pickled ginger, lime zest, cilantro, scallions, salt, and pepper in a small serving bowl for the pickled ginger tartar sauce. Set aside.

For the wasabi guacamole, add avocado, tomato, garlic, lime zest and juice, wasabi powder, cilantro, salt, and pepper to a small serving bowl.

Mash together until smooth. Set aside.

For the tempura batter/tuna, whisk all-purpose flour, rice flour, eggs, cold soda water, salt, fish sauce, sesame oil, and sesame seeds together in a large bowl, but do not over mix.

Keep the batter well chilled in the refrigerator or over an ice bath until ready to use.

In a deep-fryer or stockpot, heat the oil to 350 to 375 degrees F.

Cut the sushi-grade ahi tuna into 2 portions.

Dip each piece of tuna into the tempura batter, coating all sides.

Lower into the deep-fryer and cook until the batter is crisp, but not overly browned, approximately 1 minute.

Remove from the fryer to a cutting board and cut into 1/4 to 1/2-inch slices.

Transfer the tuna to a serving platter and serve with the pickled ginger tartar sauce and the wasabi guacamole.