For the tartare:
Dice the tuna into small pieces. Finely chop the gherkins, capers and shallot and add to the tuna. Mix in the olive oil, lemon juice, salt and pepper. Form into quenelles and store in the refrigerator. Cut the pappadams into 4 and deep-fry until golden.
For the beet pickle:
Cut the beet into small dice and add to a saucepan with the rest of the ingredients except for the mustard. Cook on low heat until the beets are semisoft. Remove from the heat and allow the beets to cool in the liquid. Mix in the mustard.
Stack the tuna quenelles in layers on top of the pappadams and arrange the beets around the side. Finish with a drizzle of truffle oil, a sprig of dill and a capperberry on top of the tuna.