Gently score the top of each shiitake mushroom cap with a crisscross pattern.
Heat the oil in a large skillet over medium heat.
Add the mushrooms and cook for 2-3 minutes, just until fragrant.
Remove from the heat and set aside to cool.
While the mushrooms cool, cut the nori sheet crosswise into 8 thin, equal strips.
Moisten your hands with water to prevent the rice from sticking. Scoop about 2 tablespoons (30 ml / 1 fl oz) of sushi rice and gently shape it into a small, rectangular mound in your palm.
Repeat to create 8 rice beds.
Place one cooled shiitake mushroom on top of each rice bed. For a fun visual twist, place half of them cap-side up and half cap-side down.
Wrap a nori strip around the center of each piece of nigiri, like a little seatbelt, to secure the mushroom to the rice. Moisten the end of the nori strip with a dab of water to seal it.
Arrange the finished nigiri on a platter.
Garnish with a sprinkle of Tomato Furikake, a touch of grated ginger, and sliced green onions.
Serve immediately for the best texture and flavor.
Don't limit yourself to shiitake! Delicate enoki mushrooms offer a subtle taste, while robust shimeji mushrooms provide a heartier, earthier flavor.
Keep a small bowl of water (tezu) nearby to dip your fingers in while shaping the rice. This is the secret to preventing it from sticking to your hands.
