For the guacamole:
1) Add all the ingredients to a small serving bowl.
2) Mash together until smooth. Set aside.
For the tempura batter:
1) Whisk all ingredients together in a large bowl, but do not over mix.
2) Keep well chilled in the refrigerator or over an ice bath until ready to use.
For the tuna:
1) In a deep-fryer or stockpot, heat the oil to 180C to 190C. Cut the tuna into 2 portions. Dip each piece into the tempura batter, coating all of the sides.
2) Lower the tuna 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 0.5cm to 1cm slices.
3) Transfer the tuna to a serving platter and serve with the tartar sauce and the guacamole.
This recipe was provided by professional chefs and has been scaled down from a bulk recipe provided by a restaurant. The Food Network chefs have not tested this recipe, in the proportions indicated, and therefore we cannot make any representation as to the results.