For the Tuna
Note: To dice the tuna it is best to put the tuna in the freezer for 15 minutes to firm up. If the avocado is fresh that too can be cooled to make dicing easier. Dice both into equal sizes -- about 1/4".
For the Kaffir Syrup
Combine all of the ingredients for the kaffir syrup in a small saucepan and bring to a boil. Remove from heat and let cool to room temperature. Strain and set aside.
For the Ginger Marinade
In a blender, purée the ginger with 1 tablespoon of the olive oil; add more olive oil as necessary until the ginger purée is very smooth. Transfer to a bowl and stir in the Champagne vinegar, soy sauce and 1/4 cup of the Kaffir Syrup. Set aside.
For the Tuna Tartare
Using a very sharp knife, slice the tuna steak horizontally 1/4-inch thick, then slice the tuna into 1/4 inch dice. In a bowl, gently toss the tuna dice with the olive oil, Thai chile and minced shallot. Lightly season with salt.
For the Avocado and Radish
Slice radishes with a mandolin or truffle slicer very thin. Add the radishes to ice water for 2 hours. This will crisp the radish slices and give them a nicer shape for final preparation.
In a medium bowl, gently toss the diced avocados with the olive oil and season to taste with lime juice and salt. Drain the radishes and pat dry. In a bowl, toss the radishes with a few drops of Chinese chili oil and season with salt. Mound the avocado mixture in four bowls. Arrange the tuna on top in bundles. Arrange the radishes on top of thw tuna in a decorative presentation. Spoon 3 tablespoons of Ginger Marinade around each salad and drizzle with a few drops of Chinese chili oil. Serve at once.
