1 Place sushi rice in a sieve and rinse with cold water until the water runs clear. Drain in a sieve for about 20 minutes. Place rice and 250 ml (approximately 1 cup) water in a pot and bring to a boil.
2 Cook uncovered for 2 minutes, then cover and cook until rice is tender and liquid is almost completely absorbed, about 20 minutes. Remove the pot from the heat. Remove lid and cover with a kitchen towel. Let stand for 10 minutes.
3 In a small pot, combine rice vinegar, mirin, sugar and 1 teaspoon salt. Bring to a simmer, stirring until the sugar and salt have dissolved. Place the rice in a bowl and fluff with a fork so that it cools faster. Pour the vinegar mixture on the rice and let cool completely, about 30 minutes.
4 Peel daikon radish and very thinly slice with a mandoline or peeler. Place in a sieve, sprinkle with a little salt and let drain.
5 Rinse tuna, pat dry and cut into fine dice.
6 Rinse scallions, pat dry and cut into thin slices. Rinse chile pepper, wipe dry, halve lengthwise and remove the seeds. Finely chop chile. Squeeze juice from lime half.
7 Combine tuna, scallion, chile pepper, sesame oil, 1 teaspoon soy sauce, and 1 tablespoon lime juice in a bowl and mix thoroughly. Season with salt and pepper.
8 Halve avocado lengthwise, remove pit, slice the flesh with a knife and scoop flesh out of the skin. (Alternately, you can peel the avocado before slicing.) Sprinkle avocado with some of the remaining lime juice. Rinse cilantro and shake dry.
9 Cut the nori in half diagonally.
10 With moistened hands, shape the rice into 6 small balls (about the size of ping-pong balls). Holding a half sheet of nori on your palm, place a rice ball in the center of the sheet and brush with a little wasabi paste.
11 Add about 2 tablespoons of tuna tartare, 2-3 avocado slices and 1 sprig of cilantro. Roll the nori into a cone shape, pressing the rice a bit flat.
12 Tuck some radish slices in the top of the cone. Repeat with remaining ingredients to make 5 more hand rolls. Serve with pickled ginger and more soy sauce.