Warm the unagi fillet as per package instructions and cut it in half lengthwise. Slice the cucumber lengthwise and cut the avocado into 1cm wide slices.

In a bowl, mix the vinegar, sugar, and salt to prepare the sushi seasoning.

Add the sushi seasoning to the cooked rice gradually, mixing gently with a cutting motion.

In another bowl, beat the eggs and mix in the sake, soy sauce, sugar, and salt.

Heat a frying pan with salad oil and cook the egg mixture into scrambled eggs.

Place a sheet of plastic wrap on a bamboo sushi mat, then lay a sheet of nori on top. Spread the seasoned rice evenly over the nori.

Flip the nori and rice over so the rice faces the plastic wrap. Remove the top layer of plastic wrap.

Place the scrambled eggs, cucumber, and avocado near the edge closest to you. Roll tightly using the bamboo mat. Place the unagi on top of the roll and wrap again to secure.