Of course it’s not sashimi. First of all, it's mushrooms, not fish. Second of all, the mushrooms are cooked, not raw. And I’m recommending sautéeing in a skillet instead of grilling. Oh well. It’s still a lot of fun.

This will serve around six people

What You Will Need
6 portobello mushrooms, stems removed, caps cleaned
grapeseed oil
sesame oil
shoyu
wasabi

What To Do Now
Sautée the portobello caps in grapeseed oil at a medium heat for one minute. (I am recommending grapeseed oil because its flavours are neutral). While the caps are cooking, drizzle a small bit of shoyu into the gills of the mushrooms. Flip them over and sauté the gills and sprinkle a few drops of sesame oil on the caps. After another minute or so, flip the mushrooms over again. Make sure that they don’t curl. When the mushrooms are soft to the touch, transfer them to a bowl to cool slightly.

Now remove the mushrooms to a cutting board. Slice the caps into sections about ½ an inch thick. Arrange on a lacquer tray or platter.

Some juices will have leaked from the mushrooms into the bowl; to this add shoyu and wasabi and whisk with a pair of hashi (Japanese chopsticks) briefly. Pour into a dipping bowl.

The mushrooms are excellent served warm or at room temperature. You could garnish them with gomasio if you would like.