In the basement of a building connected to Tokyo's Shibuya Station is a branch of the popular sushi chain Tsukiji Sushisay ( The counter seats are lively on a Friday night with beer and sake flowing freely and jovial chefs expertly constructing custom sushi orders.

This is my second visit this month, and I've returned for one reason: avocado sushi.

Chilling behind the counter in front of me — between spiky sea urchins and rainbows of slippery slabs of fish — this creamy green vegetable is waiting to be diced into sushi, sashimi or salad.