Rinse the rice in water until it runs clear, ~3 times.
Place the rice and water in a small saucepan over high heat. Bring to boil, then reduce to simmer and cover. Cook 15 minutes, then remove from heat, and let stand for 10 more minutes.
In the meantime, combine the rice vinegar, sugar, and salt in a bowl. Mix until melted. You can use the microwave to help melt the sugar and salt by microwaving on high for 30 seconds.
When the rice is cooked, transfer to a bowl, add the vinegar mixture, and mix/fluff with a fork. Let it cool to room temperature before making the sushi.
Slice the mushrooms into 8 even strips ~¼ inch thick.
Mix the marinated mushroom ingredients (except the mushrooms) in a bowl.
Heat your grill over medium heat. Oil. Cook until you get grill marks and the mushrooms soften, ~3 minutes per side, basting with the marinade.
Split the rice into 8 equal parts. With wet hands, press each part into the side wall of a rectangular container as shown in the photo or form with your fingers. Pack it in firmly so it comes out as one piece. Repeat 7 more times. You can also form them using just your hands.
Top each rice rectangle with one piece of the cooked mushroom. Wrap each with one of the nori strips and enjoy!
Keep your hands very wet when working with the cooked sushi rice. Rice will stick to dry hands, but not wet hands.Make the rice an hour in advance so it has plenty of time to cool and you don't feel rushed.Rice forming trick: Take a rectangular/square plastic, glass, or metal container and line it with plastic wrap. With wet hands, press each part of the sushi into the side wall of a rectangular container as shown in the photo in the blog post. Pack it in firmly so it comes out as one uniform piece. You can even use an old takeout container in a pinch.Nori strips: You can cut the nori sheets using a sharp kitchen knife.