Trim the base of the king oyster mushrooms and cut them lengthwise into 2 to 4 pieces each.

Lay out the beef slices and season one side lightly with salt and pepper. Cut the beef as needed to match the number of mushroom pieces, then place a mushroom piece on each and roll up.

Make a small diagonal slit in each shishito pepper.

Heat 1/2 tablespoon of vegetable oil in a skillet over medium heat. Add the shishito peppers and sauté briefly, then remove from the pan.

Add the remaining 1 1/2 tablespoons of vegetable oil to the skillet. Place the beef rolls seam-side down in the pan and start cooking over medium heat.

After a short while, turn the rolls to brown all sides evenly.

Sprinkle the sake over the rolls, cover the pan, and steam over low heat for about 5 minutes.

Add the mirin and soy sauce to the pan, return the shishito peppers, and cook until the sauce thickens and coats the rolls. Remove from heat, plate, and serve. Sprinkle with shichimi togarashi if desired.