Sesame Lime Dressing
Trim the piece of tuna slightly so it is shaped liked a cylinder, (rolling it will also shape it). Roll in the black pepper and wrap tightly in plastic wrap, rolling into a round shape and twisting ends of plastic wrap tightly to keep round shape. Refrigerate for at least 1 hour before slicing.
Whisk scallion, lemon juice, lime zest, tamari, sesame oil and toasted black sesame seeds together and set aside.
Unwrap chilled tuna cylinder. Slice thinly. Arrange 3 to 5 slices of tuna carpaccio on each chilled plate.
Drizzle the carpaccio with the Sesame Lime Dressing and garnish each plate with cilantro, a twist of cracked pepper and some root chips.